Magnetic tape, magnetic tape cartridge, and magnetic tape device

ABSTRACT

The magnetic tape includes a non-magnetic support, and a magnetic layer including a ferromagnetic powder. The number of recesses having an equivalent circle diameter of 0.30 μm to 0.60 μm existing on a surface of the magnetic layer is 10 to 600 per 40 μm×40 μm area, and a standard deviation σ of the number of recesses in a width direction on the surface of the magnetic layer is 100 or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese Patent Application No. 2022-015601 filed on Feb. 3, 2022. The above application is hereby expressly incorporated by reference, in its entirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape, a magnetic tape cartridge, and a magnetic tape device.

Magnetic recording media are divided into tape-shaped magnetic recording media and disk-shaped magnetic recording media, and tape-shaped magnetic recording media, that is, magnetic tapes are mainly used for data storage such as data back-up or archives (for example, see JP2016-524774A and US2019/0164573A1).

SUMMARY OF THE INVENTION

The recording of data on a magnetic tape is normally performed by causing the magnetic tape to run in a magnetic tape device and causing a magnetic head to follow a data band of the magnetic tape to record data on the data band. Accordingly, a data track is formed on the data band. In addition, in a case of reproducing the recorded data, the magnetic tape is caused to run in the magnetic tape device and the magnetic head is caused to follow the data band of the magnetic tape, thereby reading data recorded on the data band.

In order to increase an accuracy with which the magnetic head follows the data band of the magnetic tape in the recording and/or the reproducing, a system that performs head tracking using a servo signal (hereinafter, referred to as a “servo system”) is practiced.

In addition, it is proposed that dimensional information of a magnetic tape during running in a width direction (contraction, expansion, or the like) is obtained using the servo signal and an angle for tilting an axial direction of a module of a magnetic head with respect to the width direction of the magnetic tape (hereinafter, also referred to as a “head tilt angle”) is changed according to the obtained dimensional information (see JP6590102B and US2019/0164573A1, for example, paragraphs 0059 to 0067 and paragraph 0084 of JP6590102B). During the recording or the reproducing, in a case where the magnetic head for recording or reproducing data records or reproduces data while being deviated from a target track position due to width deformation of the magnetic tape, phenomenons such as overwriting on recorded data, reproducing failure, and the like may occur. The present inventors consider that changing the head tilt angle as described above is one of a unit for suppressing the occurrence of such a phenomenon.

In view of the above, an object of an aspect of the invention is to provide a magnetic tape device capable of performing recording and/or reproducing in an excellent manner during recording and/or reproducing of data by changing a head tilt angle during running of a magnetic tape.

According to an aspect of the invention, there is provided a magnetic tape comprising: a non-magnetic support; and a magnetic layer containing a ferromagnetic powder, in which the number of recesses having an equivalent circle diameter of 0.30 μm to 0.60 μm existing on a surface of the magnetic layer is 10 to 600 per 40 μm×40 μm area, and a standard deviation σ of the number of recesses in a width direction on the surface of the magnetic layer is 100 or less.

In one embodiment, the number of the recesses may be 10 to 100.

In one embodiment, the standard deviation of the number of the recesses may be 20 or less.

In one embodiment, a vertical squareness ratio of the magnetic tape may be 0.60 or more.

In one embodiment, the magnetic tape may further include a non-magnetic layer containing a non-magnetic powder between the non-magnetic support and the magnetic layer.

In one embodiment, the magnetic tape may include a back coating layer containing a non-magnetic powder on a surface side of the non-magnetic support opposite to a surface side provided with the magnetic layer.

In one embodiment, the magnetic tape may have a tape thickness of 5.2 μm or less.

According to another aspect of the invention, there is provided a magnetic tape cartridge comprising the magnetic tape described above.

According to still another aspect of the invention, there is provided a magnetic tape device comprising the magnetic tape described above.

In one embodiment, the magnetic tape device may further comprise a magnetic head, the magnetic head may include a module including an element array having a plurality of magnetic head elements between a pair of servo signal reading elements, and the magnetic tape device may change an angle θ formed by an axis of the element array with respect to the width direction of the magnetic tape during running of the magnetic tape in the magnetic tape device.

According to an aspect of the disclosure, it is possible to provided a magnetic tape device capable of performing recording and/or reproducing in an excellent manner during recording and/or reproducing of data by changing a head tilt angle during running of a magnetic tape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an example of a module of a magnetic head.

FIG. 2 is an explanatory diagram of a relative positional relationship between a module and a magnetic tape during running of the magnetic tape in a magnetic tape device.

FIG. 3 is an explanatory diagram of a change in angle θ during the running of the magnetic tape.

FIG. 4 shows an example (schematic step diagram) of a magnetic tape manufacturing step.

FIG. 5 shows an example of disposition of data bands and servo bands.

FIG. 6 shows a servo pattern disposition example of a linear tape-open (LTO) Ultrium format tape.

FIG. 7 is an explanatory diagram of a method for measuring the angle θ during the running of the magnetic tape.

FIG. 8 is a schematic view showing an example of the magnetic tape device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Magnetic Tape

An aspect of the invention relates to a magnetic tape including a non-magnetic support, and a magnetic layer containing a ferromagnetic powder. The number of recesses having an equivalent circle diameter of 0.30 μm to 0.60 μm existing on a surface of the magnetic layer is 10 to 600 per 40 μm×40 μm area, and a standard deviation σ of the number of recesses in a width direction on the surface of the magnetic layer is 100 or less.

Description of Head Tilt Angle

Hereinafter, prior to the description of the magnetic tape, a configuration of the magnetic head, a head tilt angle, and the like will be described. In addition, a reason why it is considered that the phenomenon occurring during the recording or during the reproducing described above can be suppressed by tilting an axial direction of the module of the magnetic head with respect to the width direction of the magnetic tape while the magnetic tape is running will also be described later.

The magnetic head may include one or more modules including an element array having a plurality of magnetic head elements between a pair of servo signal reading elements, and can include two or more modules or three or more modules. The total number of such modules can be, for example, 5 or less, 4 or less, or 3 or less, or the magnetic head may include the number of modules exceeding the total number exemplified here. Examples of arrangement of the plurality of modules can include “recording module-reproducing module” (total number of modules: 2), “recording module-reproducing module-recording module” (total number of modules: 3), and the like. However, the invention is not limited to the examples shown here.

Each module can include an element array including a plurality of magnetic head elements between a pair of servo signal reading elements, that is, arrangement of elements. The module including a recording element as the magnetic head element is a recording module for recording data on the magnetic tape. The module including a reproducing element as the magnetic head element is a reproducing module for reproducing data recorded on the magnetic tape. In the magnetic head, the plurality of modules are arranged, for example, in a recording and reproducing head unit so that an axis of the element array of each module is oriented in parallel. The “parallel” does not mean only parallel in the strict sense, but also includes a range of errors normally allowed in the technical field of the invention. For example, the range of errors means a range of less than ±10° from an exact parallel direction.

In each element array, the pair of servo signal reading elements and the plurality of magnetic head elements (that is, recording elements or reproducing elements) are usually arranged to be in a straight line spaced apart from each other. Here, the expression that “arranged in a straight line” means that each magnetic head element is arranged on a straight line connecting a central portion of one servo signal reading element and a central portion of the other servo signal reading element. The “axis of the element array” in the present invention and the present specification means the straight line connecting the central portion of one servo signal reading element and the central portion of the other servo signal reading element.

Next, the configuration of the module and the like will be further described with reference to the drawings. However, the aspect shown in the drawings is an example and the invention is not limited thereto.

FIG. 1 is a schematic view showing an example of a module of a magnetic head. The module shown in FIG. 1 includes a plurality of magnetic head elements between a pair of servo signal reading elements (servo signal reading elements 1 and 2). The magnetic head element is also referred to as a “channel”. “Ch” in the drawing is an abbreviation for a channel. The module shown in FIG. 1 includes a total of 32 magnetic head elements of Ch0 to Ch31.

In FIG. 1 , “L” is a distance between the pair of servo signal reading elements, that is, a distance between one servo signal reading element and the other servo signal reading element. In the module shown in FIG. 1 , the “L” is a distance between the servo signal reading element 1 and the servo signal reading element 2. Specifically, the “L” is a distance between a central portion of the servo signal reading element 1 and a central portion of the servo signal reading element 2. Such a distance can be measured by, for example, an optical microscope or the like.

FIG. 2 is an explanatory diagram of a relative positional relationship between the module and the magnetic tape during running of the magnetic tape in the magnetic tape device. In FIG. 2 , a dotted line A indicates a width direction of the magnetic tape. A dotted line B indicates an axis of the element array. An angle θ can be the head tilt angle during the running of the magnetic tape, and is an angle formed by the dotted line A and the dotted line B. During the running of the magnetic tape, in a case where the angle θ is 0°, a distance in a width direction of the magnetic tape between one servo signal reading element and the other servo signal reading element of the element array (hereinafter, also referred to as an “effective distance between servo signal reading elements”) is “L”. On the other hand, in a case where the angle θ exceeds 0°, the effective distance between the servo signal reading elements is “L cos θ” and the L cos θ is smaller than the L. That is, “L cos θ<L”.

As described above, during the recording or the reproducing, in a case where the magnetic head for recording or reproducing data records or reproduces data while being deviated from a target track position due to width deformation of the magnetic tape, phenomenons such as overwriting on recorded data, reproducing failure, and the like may occur. For example, in a case where a width of the magnetic tape contracts or extends, a phenomenon may occur in which the magnetic head element that should record or reproduce at a target track position records or reproduces at a different track position. In addition, in a case where the width of the magnetic tape extends, the effective distance between the servo signal reading elements may be shortened than a spacing of two adjacent servo bands with a data band interposed therebetween (also referred to as a “servo band spacing” or “spacing of servo bands”, specifically, a distance between the two servo bands in the width direction of the magnetic tape), and a phenomenon in that the data is not recorded or reproduced at a part close to an edge of the magnetic tape can occur.

With respect to this, in a case where the element array is tilted at the angle θ exceeding 0°, the effective distance between the servo signal reading elements becomes “L cos θ” as described above. The larger the value of θ, the smaller the value of L cos θ, and the smaller the value of θ, the larger the value of L cos θ. Accordingly, in a case where the value of θ is changed according to a degree of dimensional change (that is, contraction or expansion) in the width direction of the magnetic tape, the effective distance between the servo signal reading elements can be brought closer to or matched with the spacing of the servo bands. Therefore, during the recording or the reproducing, it is possible to prevent the occurrence of phenomenons such as overwriting on recorded data, reproducing failure, and the like caused in a case where the magnetic head for recording or reproducing data records or reproduces data while being deviated from a target track position due to width deformation of the magnetic tape, or it is possible to reduce a frequency of occurrence thereof.

FIG. 3 is an explanatory diagram of a change in angle θ during the running of the magnetic tape.

The angle θ at the start of running, θ_(initial), can be set to, for example, 0° or more or more than 0°.

In FIG. 3 , a central diagram shows a state of the module at the start of running.

In FIG. 3 , a right diagram shows a state of the module in a case where the angle θ is set to an angle θ_(c) which is a larger angle than the θ_(initial). The effective distance between the servo signal reading elements L cos θ_(c) is a value smaller than L cos θ_(initial) at the start of running of the magnetic tape. In a case where the width of the magnetic tape is contracted during the running of the magnetic tape, it is preferable to perform such angle adjustment.

On the other hand, in FIG. 3 , a left diagram shows a state of the module in a case where the angle θ is set to an angle θ_(e) which is a smaller angle than the ° initial. The effective distance between the servo signal reading elements L cos θ_(e) is a value larger than L COS θ_(initial) at the start of running of the magnetic tape. In a case where the width of the magnetic tape is expanded during the running of the magnetic tape, it is preferable to perform such angle adjustment.

As described above, the change of the head tilt angle during the running of the magnetic tape can contribute to prevention of the occurrence of phenomenons such as overwriting on recorded data, reproducing failure, and the like caused in a case where the magnetic head for recording or reproducing data records or reproduces data while being deviated from a target track position due to width deformation of the magnetic tape, or to reduction of a frequency of occurrence thereof.

Meanwhile, the recording of data on the magnetic tape and the reproducing of the recorded data are performed by bringing the surface of the magnetic layer of the magnetic tape into contact with the magnetic head and sliding. In a case where the head tilt angle is changed, during the running of the magnetic tape to perform recording and/or reproducing of data on the magnetic tape, a head tilt angle during the recording of data on a certain recording bit may be different from a head tilt angle during the reading (that is, during reproducing) of data from the recording bit. Accordingly, the present inventors consider that, during the data recording and the data reproducing on a certain bit, a change in a contact state between the magnetic head and the surface of the magnetic layer and a change in running frictional properties may cause a deterioration in reproducing signal quality. As a result of further intensive studies, the present inventors have newly found that, regarding an existence state of the recess on the surface of the magnetic layer of the magnetic tape, the number of recesses having an equivalent circle diameter of 0.30 μm to 0.60 μm existing on the surface of the magnetic layer is 10 to 600 per 40 μm×40 μm area, the standard deviation σ of the number of recesses in a width direction on the surface of the magnetic layer is 100 or less, and accordingly, in a case of performing the recording and/or reproducing of data by changing the head tilt angle during the running of the magnetic tape, it is possible to perform the recording and/or reproducing in an excellent manner.

Existence State of Recesses on Surface of Magnetic Layer

In the invention and the specification, the number of recesses having an equivalent circle diameter of 0.30 μm to 0.60 μm existing on the surface of the magnetic layer is obtained by performing measurement on the surface of the magnetic layer of the magnetic tape by using an atomic force microscope (AFM) as will be described below. In the invention and the specification, the “surface of the magnetic layer” is identical to a surface of the magnetic tape on the magnetic layer side. The number of recesses having an equivalent circle diameter of 0.30 μm to 0.60 μm existing on the surface of the magnetic layer (per 40 μm×40 μm area), which is obtained as will be described below, is also defined as simply the “number of recesses”. In addition, the standard deviation of the number of recesses, which is obtained as will be described below, is also defined as “the width direction σ of the number of recesses”.

The measurement region is a region having a size of 40 μm×40 μm. The measurement is performed at five points. The five points, where the surface of the magnetic layer is measured, are five points having the same position in a longitudinal direction and different positions in the width direction. The position in the longitudinal direction is randomly selected on the surface of the magnetic layer, the width direction is divided into five with respect to a magnetic tape width at the position in the longitudinal direction (accordingly, in a case where the magnetic tape with is defined as W, a with of each section is defined as “W/5”), and the number of recesses having an equivalent circle diameter of 0.30 μm to 0.60 μm existing on the surface of the magnetic layer is obtained in a region having 40 μm square (40 μm×40 μm) which is randomly selected in each section. An arithmetic mean of the five measurement values obtained as described above is defined as the number of recesses having an equivalent circle diameter of 0.30 μm to 0.60 μm existing on the surface of the magnetic layer of the magnetic tape to be measured (per 40 μm×40 μm area). In addition, the standard deviation σ (that is, the positive square root of the dispersion) of the five measurement values obtained as described above is defined as the standard deviation σ (the width direction σ of the number of recesses) of the number of the recesses in the width direction of the surface of the magnetic layer of the magnetic tape to be measured.

For the measurement of the number of recesses, in a plane image of the surface of the magnetic layer obtained by using the AFM, a surface of the measurement area equivalent to volumes of protrusion components and recess components is defined as a reference surface, and a portion detected as a portion recessed from this reference surface is specified as a “recess”. The portion specified as the recess may be a recess, a part of which is within the measurement area and the other part of which is beyond the measurement area. In a case of obtaining the number of recesses, the number of recesses is measured by including such a recess. In the plane image of the surface of the magnetic layer obtained by using the AFM, the area of the portion specified as the recess (hereinafter, “area A”) is measured, and an equivalent circle diameter D is calculated by (A/π){circumflex over ( )}(½)×2=D. Here, an operator “{circumflex over ( )}” represents exponentiation. The equivalent circle diameter is obtained as a value in unit of μm and calculated in 0.01 μm increments by rounding off three digits after the decimal point and rounding down four digits after the decimal point. As an example of the measurement condition of the AFM, the following measurement conditions can be used.

The measurement regarding a region of the surface of the magnetic layer of the magnetic tape having an area of 40 μm×40 μm is performed with an AFM (Nanoscope 5 manufactured by BRUKER Corporation) in a peak force tapping mode. SCANASYST-AIR manufactured by BRUKER Corporation is used as a probe, a resolution is set as 512 pixels×512 pixels, and a scan speed is set by the measurement regarding 1 screen (512 pixels×512 pixels) for 512 seconds.

Number of Recesses

The number of recesses having an equivalent circle diameter of 0.30 μm to 0.60 μm existing on the surface of the magnetic layer of the magnetic tape is 10 to 600 per 40 μm×40 μm area. The present inventors consider that the number of recesses being 600 or less can contribute to the suppression of the change in the running frictional properties described above. From this point, the number of recesses is preferably 500 or less, more preferably 400 or less, even more preferably 300 or less, still preferably 200 or less, and still more preferably 100 or less.

On the other hand, from a viewpoint of suppressing the occurrence of a deterioration in the reproducing signal due to a foreign matter called debris by reducing the contact area between the magnetic tape and the magnetic head, the number of recesses is 10 or more, preferably 20 or more, more preferably 30 or more, even more preferably 40 or more, and still preferably 50 or more.

Width Direction σ of Number of Recesses

The standard deviation σ of the number of recesses in the width direction of the surface of the magnetic layer of the magnetic tape (the width direction σ of the number of recesses) is 100 or less. The present inventors consider that this can contribute to the suppression of the change in the running frictional properties described above. From this point, the width direction σ of the number of recesses is preferably 90 or less, and is more preferably in the order of 80 or less, 70 or less, 60 or less, 50 or less, 40 or less, 30 or less, and 20 or less. The width direction σ of the number of recesses can be, for example, 0 or more, 1 or more, 3 or more, 5 or more, 7 or more, or 10 or more. From a viewpoint of further suppressing the change in the running frictional properties described above, it is surmised that the smaller the value of the width direction σ of the number of recesses is, the more preferable it is.

A method for controlling the number of recesses and a method for controlling the width direction σ of the number of recesses will be described later.

Magnetic Layer

Ferromagnetic Powder

As the ferromagnetic powder contained in the magnetic layer, a well-known ferromagnetic powder can be used as one kind or in combination of two or more kinds as the ferromagnetic powder used in the magnetic layer of various magnetic recording media. It is preferable to use a ferromagnetic powder having an average particle size as the ferromagnetic powder, from a viewpoint of improvement of a recording density. From this viewpoint, an average particle size of the ferromagnetic powder is preferably equal to or smaller than 50 nm, more preferably equal to or smaller than 45 nm, even more preferably equal to or smaller than 40 nm, further preferably equal to or smaller than 35 nm, further more preferably equal to or smaller than 30 nm, further even more preferably equal to or smaller than 25 nm, and still preferably equal to or smaller than 20 nm. Meanwhile, from a viewpoint of stability of magnetization, the average particle size of the ferromagnetic powder is preferably equal to or greater than 5 nm, more preferably equal to or greater than 8 nm, even more preferably equal to or greater than 10 nm, still preferably equal to or greater than 15 nm, and still more preferably equal to or greater than 20 nm.

Hexagonal Ferrite Powder

As a preferred specific example of the ferromagnetic powder, a hexagonal ferrite powder can be used. For details of the hexagonal ferrite powder, descriptions disclosed in paragraphs 0012 to 0030 of JP2011-225417A, paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 of JP2012-204726A, and paragraphs 0029 to 0084 of JP2015-127985A can be referred to, for example.

In the invention and the specification, the “hexagonal ferrite powder” is a ferromagnetic powder in which a hexagonal ferrite type crystal structure is detected as a main phase by X-ray diffraction analysis. The main phase is a structure to which a diffraction peak at the highest intensity in an X-ray diffraction spectrum obtained by the X-ray diffraction analysis belongs. For example, in a case where the diffraction peak at the highest intensity in the X-ray diffraction spectrum obtained by the X-ray diffraction analysis belongs to a hexagonal ferrite type crystal structure, it is determined that the hexagonal ferrite type crystal structure is detected as a main phase. In a case where only a single structure is detected by the X-ray diffraction analysis, this detected structure is set as a main phase. The hexagonal ferrite type crystal structure includes at least an iron atom, a divalent metal atom, and an oxygen atom as constituting atoms. A divalent metal atom is a metal atom which can be divalent cations as ions, and examples thereof include an alkali earth metal atom such as a strontium atom, a barium atom, or a calcium atom, and a lead atom. In the invention and the specification, the hexagonal strontium ferrite powder is powder in which a main divalent metal atom included in this powder is a strontium atom, and the hexagonal barium ferrite powder is a powder in which a main divalent metal atom included in this powder is a barium atom. The main divalent metal atom is a divalent metal atom occupying the greatest content in the divalent metal atom included in the powder based on atom %. However, the divalent metal atom described above does not include rare earth atom. The “rare earth atom” of the invention and the specification is selected from the group consisting of a scandium atom (Sc), an yttrium atom (Y), and a lanthanoid atom. The lanthanoid atom is selected from the group consisting of a lanthanum atom (La), a cerium atom (Ce), a praseodymium atom (Pr), a neodymium atom (Nd), a promethium atom (Pm), a samarium atom (Sm), an europium atom (Eu), a gadolinium atom (Gd), a terbium atom (Tb), a dysprosium atom (Dy), a holmium atom (Ho), an erbium atom (Er), a thulium atom (Tm), an ytterbium atom (Yb), and a lutetium atom (Lu).

Hereinafter, the hexagonal strontium ferrite powder which is one aspect of the hexagonal ferrite powder will be described more specifically.

An activation volume of the hexagonal strontium ferrite powder is preferably in a range of 800 to 1,600 nm³. The atomized hexagonal strontium ferrite powder showing the activation volume in the range described above is suitable for manufacturing a magnetic tape exhibiting excellent electromagnetic conversion characteristics. The activation volume of the hexagonal strontium ferrite powder is preferably equal to or greater than 800 nm³, and can also be, for example, equal to or greater than 850 nm³. In addition, from a viewpoint of further improving the electromagnetic conversion characteristics, the activation volume of the hexagonal strontium ferrite powder is more preferably equal to or smaller than 1,500 nm³, even more preferably equal to or smaller than 1,400 nm³, still preferably equal to or smaller than 1,300 nm³, still more preferably equal to or smaller than 1,200 nm³, and still even more preferably equal to or smaller than 1,100 nm³. The same applies to the activation volume of the hexagonal barium ferrite powder.

The “activation volume” is a unit of magnetization reversal and an index showing a magnetic magnitude of the particles. Regarding the activation volume and an anisotropy constant Ku which will be described later disclosed in the invention and the specification, magnetic field sweep rates of a coercivity Hc measurement part at time points of 3 minutes and 30 minutes are measured by using an oscillation sample type magnetic-flux meter (measurement temperature: 23° C.±1° C.), and the activation volume and the anisotropy constant Ku are values acquired from the following relational expression of Hc and an activation volume V. A unit of the anisotropy constant Ku is 1 erg/cc=1.0×10⁻¹ J/m³.

Hc=2Ku/Ms{1−[RkT/KuV)ln(At/0.693)]^(1/2)}

[In the expression, Ku: anisotropy constant (unit: J/m³), Ms: saturation magnetization (unit: kA/m), k: Boltzmann's constant, T: absolute temperature (unit: K), V: activation volume (unit: cm³), A: spin precession frequency (unit: s⁻¹), and t: magnetic field reversal time (unit: s)] The anisotropy constant Ku can be used as an index of reduction of thermal fluctuation, that is, improvement of thermal stability. The hexagonal strontium ferrite powder can preferably have Ku equal to or greater than 1.8×10⁵ J/m³, and more preferably have Ku equal to or greater than 2.0×10⁵ J/m³. In addition, Ku of the hexagonal strontium ferrite powder can be, for example, equal to or smaller than 2.5×10⁵ J/m³. However, the high Ku is preferable, because it means high thermal stability, and thus, Ku is not limited to the exemplified value.

The hexagonal strontium ferrite powder may or may not include the rare earth atom. In a case where the hexagonal strontium ferrite powder includes the rare earth atom, a content (bulk content) of the rare earth atom is preferably 0.5 to 5.0 atom % with respect to 100 atom % of the iron atom. In one embodiment, the hexagonal strontium ferrite powder including the rare earth atom can have a rare earth atom surface layer portion uneven distribution. The “rare earth atom surface layer portion uneven distribution” of the invention and the specification means that a content of rare earth atom with respect to 100 atom % of iron atom in a solution obtained by partially dissolving the hexagonal strontium ferrite powder with acid (hereinafter, referred to as a “rare earth atom surface layer portion content” or simply a “surface layer portion content” regarding the rare earth atom) and a content of rare earth atom with respect to 100 atom % of iron atom in a solution obtained by totally dissolving the hexagonal strontium ferrite powder with acid (hereinafter, referred to as a “rare earth atom bulk content” or simply a “bulk content” regarding the rare earth atom) satisfy a ratio of rare earth atom surface layer portion content/rare earth atom bulk content >1.0.

The content of rare earth atom of the hexagonal strontium ferrite powder which will be described later is identical to the rare earth atom bulk content. With respect to this, the partial dissolving using acid is to dissolve the surface layer portion of particles configuring the hexagonal strontium ferrite powder, and accordingly, the content of rare earth atom in the solution obtained by the partial dissolving is the content of rare earth atom in the surface layer portion of the particles configuring the hexagonal strontium ferrite powder. The rare earth atom surface layer portion content satisfying a ratio of “rare earth atom surface layer portion content/rare earth atom bulk content >1.0” means that the rare earth atoms are unevenly distributed in the surface layer portion (that is, a larger amount of the rare earth atoms is present, compared to that inside), among the particles configuring the hexagonal strontium ferrite powder. The surface layer portion of the invention and the specification means a part of the region of the particles configuring the hexagonal strontium ferrite powder towards the inside from the surface.

In a case where the hexagonal strontium ferrite powder includes the rare earth atom, a content (bulk content) of the rare earth atom is preferably in a range of 0.5 to 5.0 atom % with respect to 100 atom % of the iron atom. It is thought that the rare earth atom having the bulk content in the range described above and uneven distribution of the rare earth atom in the surface layer portion of the particles configuring the hexagonal strontium ferrite powder contribute to the prevention of a decrease in reproducing output during the repeated reproduction. It is surmised that this is because the rare earth atom having the bulk content in the range described above included in the hexagonal strontium ferrite powder and the uneven distribution of the rare earth atom in the surface layer portion of the particles configuring the hexagonal strontium ferrite powder can increase the anisotropy constant Ku. As the value of the anisotropy constant Ku is high, occurrence of a phenomenon called thermal fluctuation (that is, improvement of thermal stability) can be prevented. By preventing the occurrence of the thermal fluctuation, a decrease in reproducing output during the repeated reproduction can be prevented. It is surmised that the uneven distribution of the rare earth atom in the surface layer portion of the particles of the hexagonal strontium ferrite powder contributes to stabilization of a spin at an iron (Fe) site in a crystal lattice of the surface layer portion, thereby increasing the anisotropy constant Ku.

In addition, it is surmised that the use of the hexagonal strontium ferrite powder having the rare earth atom surface layer portion uneven distribution as the ferromagnetic powder of the magnetic layer also contributes to the prevention of chipping of the surface of the magnetic layer due to the sliding with the magnetic head. That is, it is surmised that, the hexagonal strontium ferrite powder having the rare earth atom surface layer portion uneven distribution can also contribute to the improvement of running durability of the magnetic tape. It is surmised that this is because the uneven distribution of the rare earth atom on the surface of the particles configuring the hexagonal strontium ferrite powder contributes to improvement of an interaction between the surface of the particles and an organic substance (for example, binding agent and/or additive) included in the magnetic layer, thereby improving hardness of the magnetic layer.

From a viewpoint of further preventing reduction of the reproduction output in the repeated reproduction and/or a viewpoint of further improving running durability, the content of rare earth atom (bulk content) is more preferably in a range of 0.5 to 4.5 atom %, even more preferably in a range of 1.0 to 4.5 atom %, and still preferably in a range of 1.5 to 4.5 atom %.

The bulk content is a content obtained by totally dissolving the hexagonal strontium ferrite powder. In the invention and the specification, the content of the atom is a bulk content obtained by totally dissolving the hexagonal strontium ferrite powder, unless otherwise noted. The hexagonal strontium ferrite powder including the rare earth atom may include only one kind of rare earth atom or may include two or more kinds of rare earth atom, as the rare earth atom. In a case where two or more kinds of rare earth atoms are included, the bulk content is obtained from the total of the two or more kinds of rare earth atoms. The same also applies to the other components of the invention and the specification. That is, for a given component, only one kind may be used or two or more kinds may be used, unless otherwise noted. In a case where two or more kinds are used, the content is a content of the total of the two or more kinds.

In a case where the hexagonal strontium ferrite powder includes the rare earth atom, the rare earth atom included therein may be any one or more kinds of the rare earth atom. Examples of the rare earth atom preferable from a viewpoint of further preventing reduction of the reproduction output during the repeated reproduction include a neodymium atom, a samarium atom, an yttrium atom, and a dysprosium atom, a neodymium atom, a samarium atom, an yttrium atom are more preferable, and a neodymium atom is even more preferable.

In the hexagonal strontium ferrite powder having the rare earth atom surface layer portion uneven distribution, a degree of uneven distribution of the rare earth atom is not limited, as long as the rare earth atom is unevenly distributed in the surface layer portion of the particles configuring the hexagonal strontium ferrite powder. For example, regarding the hexagonal strontium ferrite powder having the rare earth atom surface layer portion uneven distribution, a ratio of the surface layer portion content of the rare earth atom obtained by partial dissolving performed under the dissolving conditions which will be described later and the bulk content of the rare earth atom obtained by total dissolving performed under the dissolving conditions which will be described later, “surface layer portion content/bulk content” is greater than 1.0 and can be equal to or greater than 1.5. The “surface layer portion content/bulk content” greater than 1.0 means that the rare earth atoms are unevenly distributed in the surface layer portion (that is, a larger amount of the rare earth atoms is present, compared to that inside), in the particles configuring the hexagonal strontium ferrite powder. A ratio of the surface layer portion content of the rare earth atom obtained by partial dissolving performed under the dissolving conditions which will be described later and the bulk content of the rare earth atom obtained by total dissolving performed under the dissolving conditions which will be described later, “surface layer portion content/bulk content” can be, for example, equal to or smaller than 10.0, equal to or smaller than 9.0, equal to or smaller than 8.0, equal to or smaller than 7.0, equal to or smaller than 6.0, equal to or smaller than 5.0, or equal to or smaller than 4.0. However, in the hexagonal strontium ferrite powder having the rare earth atom surface layer portion uneven distribution, the “surface layer portion content/bulk content” is not limited to the exemplified upper limit or the lower limit, as long as the rare earth atom is unevenly distributed in the surface layer portion of the particles configuring the hexagonal strontium ferrite powder.

The partial dissolving and the total dissolving of the hexagonal strontium ferrite powder will be described below. Regarding the hexagonal strontium ferrite powder present as the powder, sample powder for the partial dissolving and the total dissolving are collected from powder of the same batch. Meanwhile, regarding the hexagonal strontium ferrite powder included in a magnetic layer of a magnetic tape, a part of the hexagonal strontium ferrite powder extracted from the magnetic layer is subjected to the partial dissolving and the other part is subjected to the total dissolving. The extraction of the hexagonal strontium ferrite powder from the magnetic layer can be performed by, for example, a method disclosed in a paragraph 0032 of JP2015-91747A.

The partial dissolving means dissolving performed so that the hexagonal strontium ferrite powder remaining in the solution can be visually confirmed in a case of the completion of the dissolving. For example, by performing the partial dissolving, a region of the particles configuring the hexagonal strontium ferrite powder which is 10% to 20% by mass with respect to 100% by mass of a total of the particles can be dissolved. On the other hand, the total dissolving means dissolving performed until the hexagonal strontium ferrite powder remaining in the solution is not visually confirmed in a case of the completion of the dissolving.

The partial dissolving and the measurement of the surface layer portion content are, for example, performed by the following method. However, dissolving conditions such as the amount of sample powder and the like described below are merely examples, and dissolving conditions capable of performing the partial dissolving and the total dissolving can be randomly used.

A vessel (for example, beaker) containing 12 mg of sample powder and 10 mL of hydrochloric acid having a concentration of 1 mol/L is held on a hot plate at a set temperature of 70° C. for 1 hour. The obtained solution is filtered with a membrane filter having a hole diameter of 0.1 The element analysis of the filtrate obtained as described above is performed by an inductively coupled plasma (ICP) analysis device. By doing so, the surface layer portion content of the rare earth atom with respect to 100 atom % of the iron atom can be obtained. In a case where a plurality of kinds of rare earth atoms are detected from the element analysis, a total content of the entirety of the rare earth atoms is the surface layer portion content. The same applies to the measurement of the bulk content.

Meanwhile, the total dissolving and the measurement of the bulk content are, for example, performed by the following method.

A vessel (for example, beaker) containing 12 mg of sample powder and 10 mL of hydrochloric acid having a concentration of 4 mol/L is held on a hot plate at a set temperature of 80° C. for 3 hours. After that, the process is performed in the same manner as in the partial dissolving and the measurement of the surface layer portion content, and the bulk content with respect to 100 atom % of the iron atom can be obtained.

From a viewpoint of increasing reproducing output in a case of reproducing data recorded on a magnetic tape, it is desirable that the mass magnetization σs of ferromagnetic powder included in the magnetic tape is high. In regards to this point, in hexagonal strontium ferrite powder which includes the rare earth atom but does not have the rare earth atom surface layer portion uneven distribution, σs tends to significantly decrease, compared to that in hexagonal strontium ferrite powder not including the rare earth atom. With respect to this, it is thought that, hexagonal strontium ferrite powder having the rare earth atom surface layer portion uneven distribution is also preferable for preventing such a significant decrease in σs. In one aspect, σs of the hexagonal strontium ferrite powder can be equal to or greater than 45 A×m²/kg and can also be equal to or greater than 47 A×m²/kg. On the other hand, from a viewpoint of noise reduction, σs is preferably equal to or smaller than 80 A×m²/kg and more preferably equal to or smaller than 60 A×m²/kg. σs can be measured by using a well-known measurement device capable of measuring magnetic properties such as an oscillation sample type magnetic-flux meter. In the invention and the specification, the mass magnetization σs is a value measured at a magnetic field strength of 15 kOe, unless otherwise noted. 1 [kOe]=(10⁶/4π) [A/m]

Regarding the content (bulk content) of the constituting atom in the hexagonal strontium ferrite powder, a content of the strontium atom can be, for example, in a range of 2.0 to 15.0 atom % with respect to 100 atom % of the iron atom. In one aspect, in the hexagonal strontium ferrite powder, the divalent metal atom included in this powder can be only a strontium atom. In another aspect, the hexagonal strontium ferrite powder can also include one or more kinds of other divalent metal atoms, in addition to the strontium atom. For example, the hexagonal strontium ferrite powder can include a barium atom and/or a calcium atom. In a case where the other divalent metal atom other than the strontium atom is included, a content of a barium atom and a content of a calcium atom in the hexagonal strontium ferrite powder respectively can be, for example, in a range of 0.05 to 5.0 atom % with respect to 100 atom % of the iron atom.

As the crystal structure of the hexagonal ferrite, a magnetoplumbite type (also referred to as an “M type”), a W type, a Y type, and a Z type are known. The hexagonal strontium ferrite powder may have any crystal structure. The crystal structure can be confirmed by X-ray diffraction analysis. In the hexagonal strontium ferrite powder, a single crystal structure or two or more kinds of crystal structure can be detected by the X-ray diffraction analysis. For example, in one aspect, in the hexagonal strontium ferrite powder, only the M type crystal structure can be detected by the X-ray diffraction analysis. For example, the M type hexagonal ferrite is represented by a compositional formula of AFe₁₂O₁₉. Here, A represents a divalent metal atom, in a case where the hexagonal strontium ferrite powder has the M type, A is only a strontium atom (Sr), or in a case where a plurality of divalent metal atoms are included as A, the strontium atom (Sr) occupies the hexagonal strontium ferrite powder with the greatest content based on atom % as described above. A content of the divalent metal atom in the hexagonal strontium ferrite powder is generally determined according to the type of the crystal structure of the hexagonal ferrite and is not particularly limited. The same applies to a content of an iron atom and a content of an oxygen atom. The hexagonal strontium ferrite powder at least includes an iron atom, a strontium atom, and an oxygen atom, and can also include a rare earth atom. In addition, the hexagonal strontium ferrite powder may or may not include atoms other than these atoms. As an example, the hexagonal strontium ferrite powder may include an aluminum atom (Al). A content of the aluminum atom can be, for example, 0.5 to 10.0 atom % with respect to 100 atom % of the iron atom. From a viewpoint of further preventing the reduction of the reproduction output during the repeated reproduction, the hexagonal strontium ferrite powder includes the iron atom, the strontium atom, the oxygen atom, and the rare earth atom, and a content of the atoms other than these atoms is preferably equal to or smaller than 10.0 atom %, more preferably in a range of 0 to 5.0 atom %, and may be 0 atom % with respect to 100 atom % of the iron atom. That is, in one aspect, the hexagonal strontium ferrite powder may not include atoms other than the iron atom, the strontium atom, the oxygen atom, and the rare earth atom. The content shown with atom % described above is obtained by converting a value of the content (unit: % by mass) of each atom obtained by totally dissolving the hexagonal strontium ferrite powder into a value shown as atom % by using the atomic weight of each atom. In addition, in the invention and the specification, a given atom which is “not included” means that the content thereof obtained by performing total dissolving and measurement by using an ICP analysis device is 0% by mass. A detection limit of the ICP analysis device is generally equal to or smaller than 0.01 ppm (parts per million) based on mass. The expression “not included” is used as a meaning including that a given atom is included with the amount smaller than the detection limit of the ICP analysis device. In one aspect, the hexagonal strontium ferrite powder does not include a bismuth atom (Bi).

Metal Powder

As a preferred specific example of the ferromagnetic powder, a ferromagnetic metal powder can also be used. For details of the ferromagnetic metal powder, descriptions disclosed in paragraphs 0137 to 0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A can be referred to, for example.

ε-Iron Oxide Powder

As a preferred specific example of the ferromagnetic powder, an ε-iron oxide powder can also be used. In the invention and the specification, the “ε-iron oxide powder” is a ferromagnetic powder in which an ε-iron oxide type crystal structure is detected as a main phase by X-ray diffraction analysis. For example, in a case where the diffraction peak at the highest intensity in the X-ray diffraction spectrum obtained by the X-ray diffraction analysis belongs to an ε-iron oxide type crystal structure, it is determined that the ε-iron oxide type crystal structure is detected as a main phase. As a manufacturing method of the ε-iron oxide powder, a manufacturing method from a goethite, a reverse micelle method, and the like are known. All of the manufacturing methods are well known. For the method of manufacturing the ε-iron oxide powder in which a part of Fe is substituted with substitutional atoms such as Ga, Co, Ti, Al, or Rh, a description disclosed in J. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. 51, pp. S280-5284, J. Mater. Chem. C, 2013, 1, pp. 5200-5206 can be referred, for example. However, the manufacturing method of the ε-iron oxide powder capable of being used as the ferromagnetic powder in the magnetic layer of the magnetic tape is not limited to the method described here.

An activation volume of the ε-iron oxide powder is preferably in a range of 300 to 1,500 nm³. The atomized ε-iron oxide powder showing the activation volume in the range described above is suitable for manufacturing a magnetic tape exhibiting excellent electromagnetic conversion characteristics. The activation volume of the ε-iron oxide powder is preferably equal to or greater than 300 nm³, and can also be, for example, equal to or greater than 500 nm³. In addition, from a viewpoint of further improving the electromagnetic conversion characteristics, the activation volume of the ε-iron oxide powder is more preferably equal to or smaller than 1,400 nm³, even more preferably equal to or smaller than 1,300 nm³, still preferably equal to or smaller than 1,200 nm³, and still more preferably equal to or smaller than 1,100 nm³.

The anisotropy constant Ku can be used as an index of reduction of thermal fluctuation, that is, improvement of thermal stability. The ε-iron oxide powder can preferably have Ku equal to or greater than 3.0×10⁴ J/m³, and more preferably have Ku equal to or greater than 8.0×10⁴ J/m³. In addition, Ku of the ε-iron oxide powder can be, for example, equal to or smaller than 3.0×10⁵ J/m³. However, the high Ku is preferable, because it means high thermal stability, and thus, Ku is not limited to the exemplified value.

From a viewpoint of increasing reproducing output in a case of reproducing data recorded on a magnetic tape, it is desirable that the mass magnetization σs of ferromagnetic powder included in the magnetic tape is high. In regard to this point, in one aspect, σs of the ε-iron oxide powder can be equal to or greater than 8 A×m²/kg and can also be equal to or greater than 12 A×m²/kg. On the other hand, from a viewpoint of noise reduction, σs of the ε-iron oxide powder is preferably equal to or smaller than 40 A×m²/kg and more preferably equal to or smaller than 35 A×m²/kg.

In the invention and the specification, average particle sizes of various powder such as the ferromagnetic powder and the like are values measured by the following method with a transmission electron microscope, unless otherwise noted.

The powder is imaged at an imaging magnification ratio of 100,000 with a transmission electron microscope, the image is printed onto a photographic printing paper so that a total magnification ratio of 500,000 and an image of particles configuring the powder is obtained. A target particle is selected from the obtained image of particles, an outline of the particle is traced with a digitizer, and a size of the particle (primary particle) is measured. The primary particle is an independent particle which is not aggregated.

The measurement described above is performed regarding 500 particles arbitrarily extracted. An arithmetic mean of the particle size of 500 particles obtained as described above is the average particle size of the powder. As the transmission electron microscope, a transmission electron microscope H-9000 manufactured by Hitachi, Ltd. can be used, for example. In addition, the measurement of the particle size can be performed by a well-known image analysis software, for example, image analysis software KS-400 manufactured by Carl Zeiss. The average particle size shown in examples which will be described later is a value measured by using transmission electron microscope H-9000 manufactured by Hitachi, Ltd. as the transmission electron microscope, and image analysis software KS-400 manufactured by Carl Zeiss as the image analysis software, unless otherwise noted. In the invention and the specification, the powder means an aggregate of a plurality of particles. For example, the ferromagnetic powder means an aggregate of a plurality of ferromagnetic particles. The aggregate of the plurality of particles not only includes an aspect in which particles configuring the aggregate are directly in contact with each other, but also includes an aspect in which a binding agent or an additive which will be described later is interposed between the particles. A term, particles may be used for representing the powder.

As a method for collecting a sample powder from the magnetic tape in order to measure the particle size, a method disclosed in a paragraph of 0015 of JP2011-048878A can be used, for example.

In the invention and the specification, unless otherwise noted,

-   -   (1) in a case where the shape of the particle observed in the         particle image described above is a needle shape, a fusiform         shape, or a columnar shape (here, a height is greater than a         maximum long diameter of a bottom surface), the size (particle         size) of the particles configuring the powder is shown as a         length of a major axis configuring the particle, that is, a         major axis length,     -   (2) in a case where the shape of the particle is a planar shape         or a columnar shape (here, a thickness or a height is smaller         than a maximum long diameter of a plate surface or a bottom         surface), the particle size is shown as a maximum long diameter         of the plate surface or the bottom surface, and     -   (3) in a case where the shape of the particle is a sphere shape,         a polyhedron shape, or an unspecified shape, and the major axis         configuring the particles cannot be specified from the shape,         the particle size is shown as an equivalent circle diameter. The         equivalent circle diameter is a value obtained by a circle         projection method.

In addition, regarding an average acicular ratio of the powder, a length of a minor axis, that is, a minor axis length of the particles is measured in the measurement described above, a value of (major axis length/minor axis length) of each particle is obtained, and an arithmetic mean of the values obtained regarding 500 particles is calculated. Here, unless otherwise noted, in a case of (1), the minor axis length as the definition of the particle size is a length of a minor axis configuring the particle, in a case of (2), the minor axis length is a thickness or a height, and in a case of (3), the major axis and the minor axis are not distinguished, thus, the value of (major axis length/minor axis length) is assumed as 1, for convenience.

In addition, unless otherwise noted, in a case where the shape of the particle is specified, for example, in a case of definition of the particle size (1), the average particle size is an average major axis length, and in a case of the definition (2), the average particle size is an average plate diameter. In a case of the definition (3), the average particle size is an average diameter (also referred to as an average particle diameter).

The content (filling percentage) of the ferromagnetic powder of the magnetic layer is preferably in a range of 50% to 90% by mass and more preferably in a range of 60% to 90% by mass with respect to a total mass of the magnetic layer. A high filling percentage of the ferromagnetic powder in the magnetic layer is preferable from a viewpoint of improvement of recording density.

Binding Agent

The magnetic tape may be a coating type magnetic tape, and can include a binding agent in the magnetic layer. The binding agent is one or more kinds of resin. As the binding agent, various resins normally used as a binding agent of a coating type magnetic tape can be used. As the binding agent, a resin selected from a polyurethane resin, a polyester resin, a polyamide resin, a vinyl chloride resin, an acrylic resin obtained by copolymerizing styrene, acrylonitrile, or methyl methacrylate, a cellulose resin such as nitrocellulose, an epoxy resin, a phenoxy resin, and a polyvinylalkylal resin such as polyvinyl acetal or polyvinyl butyral can be used alone or a plurality of resins can be mixed with each other to be used. Among these, a polyurethane resin, an acrylic resin, a cellulose resin, and a vinyl chloride resin are preferable. These resins may be a homopolymer or a copolymer. These resins can be used as the binding agent even in the non-magnetic layer and/or a back coating layer which will be described later.

For the binding agent described above, descriptions disclosed in paragraphs 0028 to 0031 of JP2010-24113A can be referred to. An average molecular weight of the resin used as the binding agent can be, for example, 10,000 to 200,000 as a weight-average molecular weight. The amount of the binding agent used can be, for example, 1.0 to 30.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder.

Curing Agent

A curing agent can also be used together with the resin which can be used as the binding agent. As the curing agent, in one aspect, a thermosetting compound which is a compound in which a curing reaction (crosslinking reaction) proceeds due to heating can be used, and in another aspect, a photocurable compound in which a curing reaction (crosslinking reaction) proceeds due to light irradiation can be used. At least a part of the curing agent is included in the magnetic layer in a state of being reacted (crosslinked) with other components such as the binding agent, by proceeding the curing reaction in the magnetic layer forming step. This point is the same as regarding a layer formed by using a composition, in a case where the composition used for forming the other layer includes the curing agent. The preferred curing agent is a thermosetting compound, and polyisocyanate is suitable. For the details of polyisocyanate, descriptions disclosed in paragraphs 0124 and 0125 of JP2011-216149A can be referred to. The amount of the curing agent can be, for example, 0 to 80.0 parts by mass with respect to 100.0 parts by mass of the binding agent in the magnetic layer forming composition, and is preferably 50.0 to 80.0 parts by mass, from a viewpoint of improvement of hardness of the magnetic layer.

Additives

The magnetic layer may include one or more kinds of additives, as necessary. As the additives, a commercially available product can be suitably selected and used according to the desired properties. Alternatively, a compound synthesized by a well-known method can be used as the additives. The additive can be used with a random amount. As the additives, the curing agent described above is used as an example. In addition, examples of the additive included in the magnetic layer include a non-magnetic powder (for example, inorganic powder, carbon black, or the like), a lubricant, a dispersing agent, a dispersing assistant, a fungicide, an antistatic agent, and an antioxidant. For the lubricant, a description disclosed in paragraphs 0030 to 0033, 0035, and 0036 of JP2016-126817A can be referred to. The lubricant may be included in the non-magnetic layer which will be described later. For the lubricant which may be included in the non-magnetic layer, a description disclosed in paragraphs 0030, 0031, 0034, 0035, and 0036 of JP2016-126817A can be referred to. For the dispersing agent, a description disclosed in paragraphs 0061 and 0071 of JP2012-133837A can be referred to. The dispersing agent may be added to a non-magnetic layer forming composition. For the dispersing agent which can be added to the non-magnetic layer forming composition, a description disclosed in paragraph 0061 of JP2012-133837A can be referred to. As the non-magnetic powder which may be contained in the magnetic layer, non-magnetic powder which can function as an abrasive, non-magnetic powder (for example, non-magnetic colloid particles) which can function as a projection formation agent which forms projections suitably protruded from the surface of the magnetic layer, and the like can be used. For example, for the abrasive, a description disclosed in paragraphs 0030 to 0032 of JP2004-273070A can be referred to. As the projection formation agent, colloidal particles are preferable, and from a viewpoint of availability, inorganic colloidal particles are preferable, inorganic oxide colloidal particles are more preferable, and silica colloidal particles (colloidal silica) are even more preferable. Average particle sizes of the abrasive and the projection formation agent are respectively preferably in a range of 30 to 200 nm and more preferably in a range of 50 to 100 nm.

The magnetic layer described above can be provided on the surface of the non-magnetic support directly or indirectly through the non-magnetic layer.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape may include a magnetic layer directly on the surface of the non-magnetic support or may include a magnetic layer on the surface of the non-magnetic support through the non-magnetic layer including the non-magnetic powder. The non-magnetic powder used in the non-magnetic layer may be a powder of an inorganic substance or a powder of an organic substance. In addition, carbon black and the like can be used. Examples of powder of the inorganic substance include powder of metal, metal oxide, metal carbonate, metal sulfate, metal nitride, metal carbide, and metal sulfide. The non-magnetic powder can be purchased as a commercially available product or can be manufactured by a well-known method. For details thereof, descriptions disclosed in paragraphs 0146 to 0150 of JP2011-216149A can be referred to. For carbon black which can be used in the non-magnetic layer, descriptions disclosed in paragraphs 0040 and 0041 of JP2010-24113A can be referred to. The content (filling percentage) of the non-magnetic powder of the non-magnetic layer is preferably in a range of 50% to 90% by mass and more preferably in a range of 60% to 90% by mass with respect to a total mass of the non-magnetic layer.

The non-magnetic layer can include a binding agent and can also include additives. In regards to other details of a binding agent or additives of the non-magnetic layer, the well-known technology regarding the non-magnetic layer can be applied. In addition, in regards to the type and the content of the binding agent, and the type and the content of the additive, for example, the well-known technology regarding the magnetic layer can be applied.

The non-magnetic layer of the invention and the specification also includes a substantially non-magnetic layer including a small amount of ferromagnetic powder as impurities or intentionally, together with the non-magnetic powder. Here, the substantially non-magnetic layer is a layer having a residual magnetic flux density equal to or smaller than 10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100 Oe), or a layer having a residual magnetic flux density equal to or smaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m (100 Oe). It is preferable that the non-magnetic layer does not have a residual magnetic flux density and coercivity.

Non-Magnetic Support

Next, the non-magnetic support will be described. As the non-magnetic support (hereinafter, also simply referred to as a “support”), well-known components such as polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamide imide, aromatic polyamide subjected to biaxial stretching are used. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferable. Corona discharge, plasma treatment, easy-bonding treatment, or heat treatment may be performed with respect to these supports in advance.

Back Coating Layer

The magnetic tape may or may not include a back coating layer including a non-magnetic powder on a surface side of the non-magnetic support opposite to the surface side provided with the magnetic layer. For the non-magnetic powder of the back coating layer, the above description regarding the non-magnetic powder of the non-magnetic layer can be referred to.

In a manufacturing step and the like of the magnetic tape, the surface shape of the rear surface is transferred to the surface of the magnetic layer (so-called offset) while the front surface and the rear surface of the magnetic layer are in contact with each other in a rolled state, thereby forming a recess on the surface of the magnetic layer. The rear surface is the surface of the back coating layer in a case of including the back coating layer, is a surface of the support in a case of not including the back coating layer. As an example of a method for controlling the existence state of recess on the surface of the magnetic layer, a type of component to be added to the composition for forming the back coating layer, for example, can be selected, in order to adjust the surface shape of the rear surface. From this viewpoint, as the non-magnetic powder of the back coating layer, it is preferable that carbon black and a non-magnetic powder other than carbon black are used in combination, or carbon black is used (that is, the non-magnetic powder of the back coating layer consists of carbon black). Examples of the non-magnetic powder other than carbon black include the non-magnetic powder exemplified above as one that can be contained in the non-magnetic layer. Regarding the non-magnetic powder of the back coating layer, a percentage of carbon black with respect to 100.0 parts by mass of the total amount of the non-magnetic powder is preferably in a range of 50.0 to 100.0 parts by mass, more preferably in a range of 70.0 to 100.0 parts by mass, even more preferably in a range of 90.0 to 100.0 parts by mass. In addition, it is also preferable that the total amount of the non-magnetic powder in the back coating layer is carbon black. The content (filling percentage) of the non-magnetic powder in the back coating layer is preferably in a range of 50% to 90% by mass and more preferably in a range of 60% to 90% by mass, with respect to the total mass of the back coating layer.

From a viewpoint of ease of control of the number of recesses having the equivalent circle diameter in the range described above existing on the surface of the magnetic layer, in the one embodiment, a non-magnetic powder having an average particle size of 50 nm or less is preferably used as the non-magnetic powder of the back coating layer. As the non-magnetic powder of the back coating layer, only one kind of the non-magnetic powder may be used or two or more kinds thereof may be used. In a case of using two or more kinds (for example, carbon black and a non-magnetic powder other than carbon black), the average particle size of each is preferably 50 nm or less. The average particle size of the non-magnetic powder is more preferably in a range of 10 to 50 nm and even more preferably in a range of 10 to 30 nm. In the one embodiment, a total amount of the non-magnetic powder contained in the back coating layer is carbon black and the average particle size thereof is preferably 50 nm or less.

In order to control the existence state of the recesses on the surface of the magnetic layer, the back coating layer forming composition preferably contains a component (dispersing agent) capable of increasing the dispersibility of the non-magnetic powder contained in this composition. The back coating layer forming composition more preferably contains a non-magnetic powder having an average particle size of 50 nm or less and a component capable of increasing dispersibility of this non-magnetic powder, and even more preferably contains carbon black having an average particle size of 50 nm or less and a component capable of increasing the dispersibility of carbon black.

As an example of such a dispersing agent, a compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1 can be used. The “alkyl ester anion” can also be referred to as an “alkyl carboxylate anion”.

(In Formula 1, R represents an alkyl group having 7 or more carbon atoms or a fluorinated alkyl group having 7 or more carbon atoms, and Z⁺ represents an ammonium cation.)

In addition, from a viewpoint of improving the dispersibility of carbon black, in the one embodiment, two or more kinds of components capable of forming the compound having a salt structure can be used in a case of preparing the back coating layer forming composition. Accordingly, in a case of preparing the back coating layer forming composition, at least some of these components can form the compound having the salt structure.

Unless otherwise noted, groups described below may have a substituent or may be unsubstituted. In addition, the “number of carbon atoms” of a group having a substituent means the number of carbon atoms not including the number of carbon atoms of the substituent, unless otherwise noted. In the present invention and the specification, examples of the substituent include an alkyl group (for example, an alkyl group having 1 to 6 carbon atoms), a hydroxy group, an alkoxy group (for example, an alkoxy group having 1 to 6 carbon atoms), a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, or the like), a cyano group, an amino group, a nitro group, an acyl group, a carboxy group, salt of a carboxy group, a sulfonic acid group, and salt of a sulfonic acid group.

Hereinafter, Formula 1 will be described in more detail.

In Formula 1, R represents an alkyl group having 7 or more carbon atoms or a fluorinated alkyl group having 7 or more carbon atoms. The fluorinated alkyl group has a structure in which some or all of the hydrogen atoms constituting the alkyl group are substituted with a fluorine atom. The alkyl group or fluorinated alkyl group represented by R may have a linear structure, a branched structure, may be a cyclic alkyl group or fluorinated alkyl group, and preferably has a linear structure. The alkyl group or fluorinated alkyl group represented by R may have a substituent, may be unsubstituted, and is preferably unsubstituted. The alkyl group represented by R can be represented by, for example, C_(n)H_(2n+1)—. Here, n represents an integer of 7 or more. In addition, for example, the fluorinated alkyl group represented by R may have a structure in which a part or all of the hydrogen atoms constituting the alkyl group represented by C_(n)H_(2n+1)— are substituted with a fluorine atom. The alkyl group or fluorinated alkyl group represented by R has 7 or more carbon atoms, preferably 8 or more carbon atoms, more preferably 9 or more carbon atoms, further preferably 10 or more carbon atoms, still preferably 11 or more carbon atoms, still more preferably 12 or more carbon atoms, and still even more preferably 13 or more carbon atoms. The alkyl group or fluorinated alkyl group represented by R has preferably 20 or less carbon atoms, more preferably 19 or less carbon atoms, and even more preferably 18 or less carbon atoms.

In Formula 1, Z⁺ represents an ammonium cation. Specifically, the ammonium cation has the following structure. In the present invention and the present specification, “*” in the formulas that represent a part of the compound represents a bonding position between the structure of the part and the adjacent atom.

The nitrogen cation N⁺ of the ammonium cation and the oxygen anion O⁻ in Formula 1 may form a salt bridging group to form the ammonium salt structure of the alkyl ester anion represented by Formula 1. The fact that the compound having the ammonium salt structure of the alkyl ester anion represented by Formula 1 is contained in the back coating layer can be confirmed by performing analysis with respect to the magnetic tape by X-ray photoelectron spectroscopy (electron spectroscopy for chemical analysis (ESCA)), infrared spectroscopy (IR), or the like.

In one embodiment, the ammonium cation represented by Z⁺ can be provided by, for example, the nitrogen atom of the nitrogen-containing polymer becoming a cation. The nitrogen-containing polymer means a polymer containing a nitrogen atom. In the present invention and the present specification, a term “polymer” means to include both a homopolymer and a copolymer. The nitrogen atom can be included as an atom configuring a main chain of the polymer in one aspect, and can be included as an atom constituting a side chain of the polymer in one embodiment.

As one aspect of the nitrogen-containing polymer, polyalkyleneimine can be used. The polyalkyleneimine is a ring-opening polymer of alkyleneimine and is a polymer having a plurality of repeating units represented by Formula 2.

The nitrogen atom N configuring the main chain in Formula 2 can be converted to a nitrogen cation N⁺ to provide an ammonium cation represented by Z⁺ in Formula 1. Then, an ammonium salt structure can be formed with the alkyl ester anion, for example, as follows.

Hereinafter, Formula 2 will be described in more detail.

In Formula 2, R¹ and R² each independently represent a hydrogen atom or an alkyl group, and n1 represents an integer of 2 or more.

Examples of the alkyl group represented by R¹ or R² include an alkyl group having 1 to 6 carbon atoms, preferably an alkyl group having 1 to 3 carbon atoms, more preferably a methyl group or an ethyl group, and even more preferably a methyl group. The alkyl group represented by R¹ or R² is preferably an unsubstituted alkyl group. A combination of R¹ and R² in Formula 2 is a form in which one is a hydrogen atom and the other is an alkyl group, a form in which both are hydrogen atoms, and a form in which both are an alkyl group (the same or different alkyl groups), and is preferably a form in which both are hydrogen atoms. As the alkyleneimine that provides the polyalkyleneimine, a structure of the ring that has the smallest number of carbon atoms is ethyleneimine, and the main chain of the alkyleneimine (ethyleneimine) obtained by ring opening of ethyleneimine has 2 carbon atoms. Accordingly, n1 in Formula 2 is 2 or more. n1 in Formula 2 can be, for example, 10 or less, 8 or less, 6 or less, or 4 or less. The polyalkyleneimine may be a homopolymer containing only the same structure as the repeating structure represented by Formula 2, or may be a copolymer containing two or more different structures as the repeating structure represented by Formula 2. A number average molecular weight of the polyalkyleneimine that can be used to form the compound having the ammonium salt structure of the alkyl ester anion represented by Formula 1 can be, for example, equal to or greater than 200, and is preferably equal to or greater than 300, and more preferably equal to or greater than 400. In addition, the number average molecular weight of the polyalkyleneimine can be, for example, equal to or less than 10,000, and is preferably equal to or less than 5,000 and more preferably equal to or less than 2,000.

In the present invention and the present specification, the average molecular weight (weight-average molecular weight and number average molecular weight) is measured by gel permeation chromatography (GPC) and is a value obtained by performing standard polystyrene conversion. Unless otherwise noted, the average molecular weights shown in the examples which will be described below are values (polystyrene-equivalent values) obtained by standard polystyrene conversion of the values measured under the following measurement conditions using GPC.

GPC device: HLC-8220 (manufactured by Tosoh Corporation)

Guard Column: TSK guard column Super HZM-H

Column: TSK gel Super HZ 2000, TSK gel Super HZ 4000, TSK gel Super HZ-M (manufactured by Tosoh Corporation, 4.6 mm (inner diameter)×15.0 cm, three kinds of columns are linked in series)

Eluent: Tetrahydrofuran (THF), including stabilizer (2,6-di-t-butyl-4-methylphenol)

Eluent flow rate: 0.35 mL/min

Column temperature: 40° C.

Inlet temperature: 40° C.

Refractive index (RI) measurement temperature: 40° C.

Sample concentration: 0.3% by mass

Sample injection amount: 10 μL

In addition, as the other aspect of the nitrogen-containing polymer, polyallylamine can be used. The polyallylamine is a polymer of allylamine and is a polymer having a plurality of repeating units represented by Formula 3.

The nitrogen atom N configuring an amino group of a side chain in Formula 3 can be converted to a nitrogen cation N⁺ to provide an ammonium cation represented by Z⁺ in Formula 1. Then, an ammonium salt structure can be formed with the alkyl ester anion, for example, as follows.

A weight-average molecular weight of the polyallylamine that can be used to form the compound having the ammonium salt structure of the alkyl ester anion represented by Formula 1 can be, for example, equal to or greater than 200, and is preferably equal to or greater than 1,000, and more preferably equal to or greater than 1,500. In addition, the weight-average molecular weight of the polyallylamine can be, for example, equal to or less than 15,000, and is preferably equal to or less than 10,000 and more preferably equal to or less than 8,000.

The fact that the compound having a structure derived from polyalkyleneimine or polyallylamine contained in the back coating layer as the compound having the ammonium salt structure of the alkyl ester anion represented by Formula 1 is included can be confirmed by analyzing the surface of the back coating layer by a time-of-flight secondary ion mass spectrometry (TOF-SIMS) or the like.

The compound having the ammonium salt structure of the alkyl ester anion represented by Formula 1 can be salt of a nitrogen-containing polymer and one or more fatty acids selected from the group consisting of fatty acids having 7 or more carbon atoms and fluorinated fatty acids having 7 or more carbon atoms. The nitrogen-containing polymer forming salt can be one kind or two or more kinds of nitrogen-containing polymers, and can be, for example, a nitrogen-containing polymer selected from the group consisting of polyalkyleneimine and polyallylamine. The fatty acids forming the salt can be one kind or two or more kinds of fatty acids selected from the group consisting of fatty acids having 7 or more carbon atoms and fluorinated fatty acids having 7 or more carbon atoms. The fluorinated fatty acid has a structure in which some or all of the hydrogen atoms configuring the alkyl group bonded to a carboxy group COOH in the fatty acid are substituted with fluorine atoms. For example, the salt forming reaction can easily proceed by mixing the nitrogen-containing polymer and the fatty acids described above at room temperature. The room temperature is, for example, approximately 20° C. to 25° C. In the one embodiment, one or more kinds of nitrogen-containing polymers and one or more kinds of the fatty acids described above are used as components of the back coating layer forming composition, and the salt forming reaction can proceed by mixing these in the step of preparing the back coating layer forming composition. In the one embodiment, one or more kinds of nitrogen-containing polymers and one or more kinds of the fatty acids described above are mixed to form a salt before preparing the back coating layer forming composition, and then, the back coating layer forming composition can be prepared using this salt as a component of the back coating layer forming composition. In a case where the nitrogen-containing polymer and the fatty acid are mixed to form an ammonium salt of the alkyl ester anion represented by Formula 1, the nitrogen atom configuring the nitrogen-containing polymer and the carboxy group of the fatty acid may be reacted to form the following structure, and an aspect including such structures are also included in the above compound.

Examples of the fatty acids include fatty acids having an alkyl group described above as R in Formula 1 and fluorinated fatty acids having a fluorinated alkyl group described above as R in Formula 1.

A mixing ratio of the nitrogen-containing polymer and the fatty acid used to form the compound having the ammonium salt structure of the alkyl ester anion represented by Formula 1 is preferably 10:90 to 90:10, more preferably 20:80 to 85:15, and even more preferably 30:70 to 80:20, as a mass ratio of nitrogen-containing polymer:fatty acid. In addition, the used amount of the compound having the ammonium salt structure of the alkyl ester anion represented by Formula 1 can be, for example, 1.0 to 20.0 parts by mass and is preferably 1.0 to 10.0 parts by mass with respect to 100.0 parts by mass of carbon black, during preparation of the back coating layer forming composition. In addition, for example, in a case of preparing the back coating layer forming composition, 0.1 to 10.0 parts by mass of the nitrogen-containing polymer can be used and 0.2 to 8.0 parts by mass of the nitrogen-containing polymer is preferably used with respect to 100.0 parts by mass of carbon black. The used amount of the fatty acids described above can be, for example, 0.05 to 10.0 parts by mass and is preferably 0.1 to 5.5 parts by mass, with respect to 100.0 parts by mass of carbon black.

For the component contained in the back coating layer, the back coating layer can include a binding agent and can also include an additive. In regards to the binding agent included in the back coating layer and additives, a well-known technology regarding the back coating layer can be applied, and a well-known technology regarding the list of the magnetic layer and/or the non-magnetic layer can also be applied. For example, for the back coating layer, descriptions disclosed in paragraphs 0018 to 0020 of JP2006-331625A and page 4, line 65, to page 5, line 38, of U.S. Pat. No. 7,029,774B can be referred to.

Various Thicknesses

Regarding a thickness (total thickness) of the magnetic tape, it has been required to increase recording capacity (increase in capacity) of the magnetic recording medium along with the enormous increase in amount of information in recent years. Regarding a tape-shaped magnetic recording medium (that is, a magnetic tape), as a unit for increasing the capacity, the thickness of the magnetic tape is decreased and a length of the magnetic tape accommodated in one roll of a magnetic tape cartridge is increased. From this point, the thickness (total thickness) of the magnetic tape is preferably 5.6 μm or less, more preferably 5.5 μm or less, even more preferably 5.4 μm or less, still preferably 5.3 μm or less, and still more preferably 5.2 μm or less. In addition, from a viewpoint of ease of handling, the thickness of the magnetic tape is preferably 3.0 μm or more and more preferably 3.5 μm or more.

The thickness (total thickness) of the magnetic tape can be measured by the following method.

Ten samples (for example, 5 to 10 cm in length) are cut out from any portion of the magnetic tape, and the samples are stacked to measure the thickness. A value (thickness per sample) obtained by calculating 1/10 of the measured thickness is set as the total thickness. The thickness measurement can be performed using a well-known measurement device capable of performing the thickness measurement at 0.1 μm order.

A thickness of the non-magnetic support is preferably 3.0 to 5.0 μm.

A thickness of the magnetic layer can be optimized according to a saturation magnetization amount of a magnetic head used, a head gap length, a recording signal band, and the like, is normally 0.01 μm to 0.15 μm, and is preferably 0.02 μm to 0.12 μm and more preferably 0.03 μm to 0.1 μm, from a viewpoint of realization of high-density recording. The magnetic layer may be at least single layer, the magnetic layer may be separated into two or more layers having different magnetic properties, and a configuration of a well-known multilayered magnetic layer can be applied. A thickness of the magnetic layer in a case where the magnetic layer is separated into two or more layers is the total thickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm and is preferably 0.1 to 1.0 μm.

A thickness of the back coating layer is preferably equal to or smaller than 0.9 μm and even more preferably 0.1 to 0.7 μm.

Various thicknesses such as the thickness of the magnetic layer and the like can be obtained by the following method.

A cross section of the magnetic tape in the thickness direction is exposed with an ion beam and the cross section observation of the exposed cross section is performed using a scanning electron microscope or a transmission electron microscope. Various thicknesses can be obtained as the arithmetic average of the thicknesses obtained at two random portions in the cross section observation. Alternatively, various thicknesses can be obtained as a designed thickness calculated under the manufacturing conditions.

Manufacturing Step

Preparation of Each Layer Forming Composition Composition for forming the magnetic layer, the non-magnetic layer, or the back coating layer generally includes a solvent, together with the various components described above. As the solvent, one kind or two or more kinds of various kinds of solvents usually used for producing a coating type magnetic recording medium can be used. The content of the solvent in each layer forming composition is not particularly limited. For the solvent, a description disclosed in a paragraph 0153 of JP2011-216149A can be referred to. A concentration of solid content and a solvent composition in each layer forming composition may be suitably adjusted according to handleability of the composition, coating conditions, and a thickness of each layer to be formed. A step of preparing a composition for forming the magnetic layer, the non-magnetic layer or the back coating layer can generally include at least a kneading step, a dispersing step, and a mixing step provided before and after these steps, in a case where necessary. Each step may be divided into two or more stages. Various components used in the preparation of each layer forming composition may be added at the beginning or during any step. In addition, each component may be separately added in two or more steps. For example, a binding agent may be separately added in a kneading step, a dispersing step, and a mixing step for adjusting viscosity after the dispersion. In the manufacturing step of the magnetic tape, a well-known manufacturing technology of the related art can be used as a part of step. In the kneading step, an open kneader, a continuous kneader, a pressure kneader, or a kneader having a strong kneading force such as an extruder can be used. The details of the kneading step are disclosed in JP1989-106338A (JP-H01-106338A) and JP1989-79274A (JP-H01-79274A). As a disperser, various well-known dispersers using a shear force such as a beads mill, a ball mill, a sand mill, or a homogenizer can be used. In the dispersion, the dispersion beads can be preferably used. As dispersion beads, ceramic beads or glass beads are used and zirconia beads are preferable. A combination of two or more kinds of beads may be used. A bead diameter (particle diameter) and a beads filling percentage of the dispersion beads are not particularly limited and may be suitably set according to powder which is a dispersion target. Each layer forming composition may be filtered by a well-known method before performing the coating step. The filtering can be performed by using a filter, for example. As the filter used in the filtering, a filter having a hole diameter of 0.01 to 3 μm (for example, filter made of glass fiber or filter made of polypropylene) can be used, for example.

Coating Step, Cooling Step, Heating and Drying Step

The magnetic layer can be formed by directly applying the magnetic layer forming composition onto the non-magnetic support or performing multilayer coating of the magnetic layer forming composition with the non-magnetic layer forming composition in order or at the same time. For details of the coating for forming each layer, a description disclosed in a paragraph 0066 of JP2010-231843A can be referred to.

As described above, in one embodiment, the magnetic tape includes the non-magnetic layer between the non-magnetic support and the magnetic layer. Such a magnetic tape can be preferably manufactured by successive multilayer coating. A manufacturing step of performing the successive multilayer coating can be preferably performed as follows. The non-magnetic layer is formed through a coating step of applying a non-magnetic layer forming composition onto a non-magnetic support to form a coating layer, and a heating and drying step of drying the formed coating layer by a heat treatment. In addition, the magnetic layer is formed through a coating step of applying a magnetic layer forming composition onto the formed non-magnetic layer to form a coating layer, and a heating and drying step of drying the formed coating layer by a heat treatment.

The present inventors consider that, in a non-magnetic layer forming step of the manufacturing method for performing the successive multilayer coating, a coating layer formed by performing a coating step by using a non-magnetic layer forming composition and a cooling step of cooling the coating layer performed between the coating step and the heating and drying step are preferable, in order to suppress the width direction σ of the number of recesses to 100 or less.

Hereinafter, an example of the manufacturing step of the magnetic tape will be described with reference to FIG. 4 . However, the invention is not limited to the following examples.

FIG. 4 is a step schematic view showing an example of a step of manufacturing the magnetic tape including a non-magnetic layer and a magnetic layer in this order on one surface of a non-magnetic support and including a back coating layer on the other surface thereof. In the example shown in FIG. 4 , an operation of sending a non-magnetic support (elongated film) from a sending part and winding the non-magnetic support around a winding part is continuously performed, and various processes of coating, drying, and alignment are performed in each part or each zone shown in FIG. 4 , and thus, it is possible to form a non-magnetic layer and a magnetic layer on one surface of the running non-magnetic support by sequential multilayer coating and to form a back coating layer on the other surface thereof. In the example shown in FIG. 4 , the manufacturing step which is normally performed for manufacturing the coating type magnetic recording medium can be performed in the same manner except for including a cooling zone.

The non-magnetic layer forming composition is applied onto the non-magnetic support sent from the sending part in a first coating part (coating step of non-magnetic layer forming composition).

After the coating step, a coating layer of the non-magnetic layer forming composition formed in the coating step is cooled in a cooling zone (cooling step). For example, it is possible to perform the cooling step by allowing the non-magnetic support on which the coating layer is formed to pass through a cooling atmosphere. An atmosphere temperature of the cooling atmosphere is preferably −10° C. to 0° C. and more preferably −5° C. to 0° C. The time for performing the cooling step (for example, time while any part of the coating layer is delivered to and sent from the cooling zone (hereinafter, also referred to as a “retention time”)) is not particularly limited. As the retention time is long, the value of the width direction σ of the number of recesses tends to be small. In the cooling step, cooled air may blow to the surface of the coating layer.

After the cooling zone, in a first heat treatment zone, the coating layer is heated after the cooling step to dry the coating layer (heating and drying step). The heating and drying process can be performed by causing the non-magnetic support including the coating layer after the cooling step to pass through the heated atmosphere. The atmosphere temperature of the heated atmosphere here, and the atmosphere temperature of the heated atmosphere in the heating and drying step in a second heat treatment zone and the heating and drying step in a three heat treatment zone which will be described later are also referred to as a “drying temperature”. The increasing of the drying temperature in each heat treatment zone can contribute to reducing of the value of the width direction σ of the number of recesses. From this viewpoint, the drying temperature in each heat treatment zone is preferably 95° C. or higher and more preferably 100° C. or higher. In addition, the drying temperature in each heat treatment zone can be, for example, 140° C. to 130° C., and can be higher than the temperature listed here. In addition, the heated air may randomly blow to the surface of the coating layer.

Next, in a second coating part, the magnetic layer forming composition is applied onto the non-magnetic layer formed by performing the heating and drying step in the first heat treatment zone (coating step of magnetic layer forming composition).

After that, in the aspect of performing the alignment process, while the coating layer of the magnetic layer forming composition is wet, an alignment process of the ferromagnetic powder in the coating layer is performed in an alignment zone. For the alignment process, various technologies disclosed in a paragraph 0067 of JP2010-231843A can be applied. For example, a homeotropic alignment process can be performed by a well-known method such as a method using a different polar facing magnet. In the alignment zone, a drying speed of the coating layer can be controlled by a temperature, an air flow of the dry air and/or a transporting rate of the magnetic tape in the alignment zone. In addition, the coating layer may be preliminarily dried before transporting to the alignment zone.

The coating layer after the alignment process is subjected to the heating and drying step in the second heat treatment zone.

Next, in the third coating part, a back coating layer forming composition is applied to a surface of the non-magnetic support on a side opposite to the surface where the non-magnetic layer and the magnetic layer are formed, to form a coating layer (coating step of back coating layer forming composition). After that, the coating layer is heated and dried in the third heat treatment zone.

By the step described above, it is possible to obtain the magnetic tape including the non-magnetic layer and the magnetic layer in this order on one surface side of the non-magnetic support and including the back coating layer on the other surface side thereof

Other Steps

In the step of manufacturing the magnetic tape, a calendar process is usually performed to increase the surface smoothness of the magnetic tape. The enhancement of the calendar process conditions can contribute to reducing of the value of the width direction σ of the number of recesses. Specific examples of the enhancement of the calendar process conditions include increasing a calendar pressure, increasing a calendar temperature, and decreasing a calendar speed. For calendar process conditions, a calendar pressure (linear pressure) is preferably 300 to 500 kN/m, more preferably 310 to 350 kN/m, the calendar temperature (surface temperature of a calendar roll) is preferably 95° C. to 120° C. and more preferably 100° C. to 120° C., and the calendar speed is preferably 50 to 75 m/min.

For various other steps for manufacturing a magnetic tape, a description disclosed in paragraphs 0067 to 0070 of JP2010-231843A can be referred to.

Through various steps, a long magnetic tape raw material can be obtained. The obtained magnetic tape raw material is, for example, cut (slit) by a well-known cutter to have a width of a magnetic tape to be accommodated around the magnetic tape cartridge. The width can be determined according to the standard and is normally ½ inches. 1 inch=2.54 cm.

In the magnetic tape obtained by slitting, normally, a servo pattern can be formed.

Formation of Servo Pattern

The “formation of the servo pattern” can be “recording of a servo signal”. The formation of the servo pattern will be described below.

The servo pattern is generally formed along a longitudinal direction of the magnetic tape. As a system of control using a servo signal (servo control), timing-based servo (TB S), amplitude servo, or frequency servo is used.

As shown in European Computer Manufacturers Association (ECMA)-319 (June 2001), a timing-based servo system is used in a magnetic tape based on a linear tape-open (LTO) standard (generally referred to as an “LTO tape”). In this timing-based servo system, the servo pattern is configured by continuously disposing a plurality of pairs of magnetic stripes (also referred to as “servo stripes”) not parallel to each other in a longitudinal direction of the magnetic tape. In the invention and the specification, the “timing-based servo pattern” refers to a servo pattern that enables head tracking in a servo system of a timing-based servo system. As described above, a reason for that the servo pattern is configured with one pair of magnetic stripes not parallel to each other is because a servo signal reading element passing on the servo pattern recognizes a passage position thereof. Specifically, one pair of the magnetic stripes are formed so that a gap thereof is continuously changed along the width direction of the magnetic tape, and a relative position of the servo pattern and the servo signal reading element can be recognized, by the reading of the gap thereof by the servo signal reading element. The information of this relative position can realize the tracking of a data track. Accordingly, a plurality of servo tracks are generally set on the servo pattern along the width direction of the magnetic tape.

The servo band is configured of servo patterns continuous in the longitudinal direction of the magnetic tape. A plurality of servo bands are normally provided on the magnetic tape. For example, the number thereof is 5 in the LTO tape. A region interposed between two adjacent servo bands is a data band. The data band is configured of a plurality of data tracks and each data track corresponds to each servo track.

In one aspect, as shown in JP2004-318983A, information showing the number of servo band (also referred to as “servo band identification (ID)” or “Unique Data Band Identification Method (UDIM) information”) is embedded in each servo band. This servo band ID is recorded by shifting a specific servo stripe among the plurality of pair of servo stripes in the servo band so that the position thereof is relatively deviated in the longitudinal direction of the magnetic tape. Specifically, the position of the shifted specific servo stripe among the plurality of pair of servo stripes is changed for each servo band. Accordingly, the recorded servo band ID becomes unique for each servo band, and therefore, the servo band can be uniquely specified by only reading one servo band by the servo signal reading element.

In a method of uniquely specifying the servo band, a staggered method as shown in ECMA-319 (June 2001) is used. In this staggered method, a plurality of the groups of one pair of magnetic stripes (servo stripe) not parallel to each other which are continuously disposed in the longitudinal direction of the magnetic tape is recorded so as to be shifted in the longitudinal direction of the magnetic tape for each servo band. A combination of this shifted servo band between the adjacent servo bands is set to be unique in the entire magnetic tape, and accordingly, the servo band can also be uniquely specified by reading of the servo pattern by two servo signal reading elements.

In addition, as shown in ECMA-319 (June 2001), information showing the position in the longitudinal direction of the magnetic tape (also referred to as “Longitudinal Position (LPOS) information”) is normally embedded in each servo band. This LPOS information is recorded so that the position of one pair of servo stripes is shifted in the longitudinal direction of the magnetic tape, in the same manner as the UDIM information. However, unlike the UDIM information, the same signal is recorded on each servo band in this LPOS information.

Other information different from the UDIM information and the LPOS information can be embedded in the servo band. In this case, the embedded information may be different for each servo band as the UDIM information, or may be common in all of the servo bands, as the LPOS information.

In addition, as a method of embedding the information in the servo band, a method other than the method described above can be used. For example, a predetermined code may be recorded by thinning out a predetermined pair among the group of pairs of the servo stripes.

A servo pattern forming head is also referred to as a servo write head. The servo write head generally includes pairs of gaps corresponding to the pairs of magnetic stripes by the number of servo bands. In general, a core and a coil are respectively connected to each of the pairs of gaps, and a magnetic field generated in the core can generate leakage magnetic field in the pairs of gaps, by supplying a current pulse to the coil. In a case of forming the servo pattern, by inputting a current pulse while causing the magnetic tape to run on the servo write head, the magnetic pattern corresponding to the pair of gaps is transferred to the magnetic tape, and the servo pattern can be formed. A width of each gap can be suitably set in accordance with a density of the servo pattern to be formed. The width of each gap can be set as, for example, equal to or smaller than 1 μm, 1 to 10 μm, or equal to or greater than 10

Before forming the servo pattern on the magnetic tape, a demagnetization (erasing) process is generally performed on the magnetic tape. This erasing process can be performed by applying a uniform magnetic field to the magnetic tape by using a DC magnet and an AC magnet. The erasing process includes direct current (DC) erasing and alternating current (AC) erasing. The AC erasing is performed by slowly decreasing an intensity of the magnetic field, while reversing a direction of the magnetic field applied to the magnetic tape. Meanwhile, the DC erasing is performed by applying the magnetic field in one direction to the magnetic tape. The DC erasing further includes two methods. A first method is horizontal DC erasing of applying the magnetic field in one direction along a longitudinal direction of the magnetic tape. A second method is vertical DC erasing of applying the magnetic field in one direction along a thickness direction of the magnetic tape. The erasing process may be performed with respect to all of the magnetic tape or may be performed for each servo band of the magnetic tape.

A direction of the magnetic field to the servo pattern to be formed is determined in accordance with the direction of erasing. For example, in a case where the horizontal DC erasing is performed to the magnetic tape, the formation of the servo pattern is performed so that the direction of the magnetic field and the direction of erasing is opposite to each other. Accordingly, the output of the servo signal obtained by the reading of the servo pattern can be increased. As disclosed in JP2012-53940A, in a case where the magnetic pattern is transferred to the magnetic tape subjected to the vertical DC erasing by using the gap, the servo signal obtained by the reading of the formed servo pattern has a unipolar pulse shape. Meanwhile, in a case where the magnetic pattern is transferred to the magnetic tape subjected to the horizontal DC erasing by using the gap, the servo signal obtained by the reading of the formed servo pattern has a bipolar pulse shape.

<Vertical Squareness Ratio>

In one embodiment, the vertical squareness ratio of the magnetic tape can be, for example, 0.55 or more, and is preferably 0.60 or more. It is preferable that the vertical squareness ratio of the magnetic tape is 0.60 or more, from a viewpoint of improving the electromagnetic conversion characteristics. In principle, an upper limit of the squareness ratio is 1.00 or less. The vertical squareness ratio of the magnetic tape can be 1.00 or less, 0.95 or less, 0.90 or less, 0.85 or less, or 0.80 or less. It is preferable that the value of the vertical squareness ratio of the magnetic tape is large from a viewpoint of improving the electromagnetic conversion characteristics. The vertical squareness ratio of the magnetic tape can be controlled by a well-known method such as performing a homeotropic alignment process.

In the invention and the specification, the “vertical squareness ratio” is squareness ratio measured in the vertical direction of the magnetic tape. The “vertical direction” described with respect to the squareness ratio is a direction orthogonal to the surface of the magnetic layer, and can also be referred to as a thickness direction. In the invention and the specification, the vertical squareness ratio is obtained by the following method.

A sample piece having a size that can be introduced into an oscillation sample type magnetic-flux meter is cut out from the magnetic tape to be measured. Regarding the sample piece, using the oscillation sample type magnetic-flux meter, a magnetic field is applied to a vertical direction of a sample piece (direction orthogonal to the surface of the magnetic layer) with a maximum applied magnetic field of 3979 kA/m, a measurement temperature of 296 K, and a magnetic field sweep speed of 8.3 kA/m/sec, and a magnetization strength of the sample piece with respect to the applied magnetic field is measured. The measured value of the magnetization strength is obtained as a value after diamagnetic field correction and a value obtained by subtracting magnetization of a sample probe of the oscillation sample type magnetic-flux meter as background noise. In a case where the magnetization strength at the maximum applied magnetic field is Ms and the magnetization strength at zero applied magnetic field is Mr, the squareness ratio SQ is a value calculated as SQ=Mr/Ms. The measurement temperature is referred to as a temperature of the sample piece, and by setting the atmosphere temperature around the sample piece to a measurement temperature, the temperature of the sample piece can be set to the measurement temperature by realizing temperature equilibrium.

Magnetic Tape Cartridge

According to another aspect of the invention, there is provided a magnetic tape cartridge comprising the magnetic tape described above.

The details of the magnetic tape included in the magnetic tape cartridge are as described above. The magnetic tape cartridge can be attached to a magnetic tape device provided with a magnetic head and used for performing the recording and/or reproducing of data.

In the magnetic tape cartridge, the magnetic tape is generally accommodated in a cartridge main body in a state of being wound around a reel. The reel is rotatably provided in the cartridge main body. As the magnetic tape cartridge, a single reel type magnetic tape cartridge including one reel in a cartridge main body and a twin reel type magnetic tape cartridge including two reels in a cartridge main body are widely used. In a case where the single reel type magnetic tape cartridge is mounted in the magnetic tape device in order to record and/or reproduce data on the magnetic tape, the magnetic tape is drawn from the magnetic tape cartridge and wound around the reel on the magnetic tape device side. A magnetic head is disposed on a magnetic tape transportation path from the magnetic tape cartridge to a winding reel. Feeding and winding of the magnetic tape are performed between a reel (supply reel) on the magnetic tape cartridge side and a reel (winding reel) on the magnetic tape device side. In the meantime, for example, the magnetic head comes into contact with and slides on the surface of the magnetic layer of the magnetic tape, and accordingly, the recording and/or reproducing of data is performed. With respect to this, in the twin reel type magnetic tape cartridge, both reels of the supply reel and the winding reel are provided in the magnetic tape cartridge.

In one aspect, the magnetic tape cartridge can include a cartridge memory. The cartridge memory can be, for example, a non-volatile memory, and in one embodiment, head tilt angle adjustment information is recorded in advance or head tilt angle adjustment information is recorded. The head tilt angle adjustment information is information for adjusting the head tilt angle during the running of the magnetic tape in the magnetic tape device. For example, as the head tilt angle adjustment information, a value of the servo band spacing at each position in the longitudinal direction of the magnetic tape at the time of data recording can be recorded. For example, in a case where the data recorded on the magnetic tape is reproduced, the value of the servo band spacing is measured at the time of the reproducing, and the head tilt angle θ can be changed by the control device of the magnetic tape device so that an absolute value of a difference of the servo band spacing at the time of recording at the same longitudinal position recorded in the cartridge memory is close to 0. The head tilt angle can be, for example, the angle θ described above.

The magnetic tape and the magnetic tape cartridge can be suitably used in the magnetic tape device (that is, magnetic recording and reproducing system) for performing recording and/or reproducing data at different head tilt angles. In such a magnetic tape device, in one embodiment, it is possible to perform the recording and/or reproducing of data by changing the head tilt angle during running of a magnetic tape. For example, the head tilt angle can be changed according to dimensional information of the magnetic tape in the width direction obtained while the magnetic tape is running. In addition, for example, in a usage aspect, a head tilt angle during the recording and/or reproducing at a certain time and a head tilt angle during the recording and/or reproducing at the next time and subsequent times are changed, and then the head tilt angle may be fixed without changing during the running of the magnetic tape for the recording and/or reproducing of each time.

Magnetic Tape Device

According to still another aspect of the invention, there is provided a magnetic tape device comprising the magnetic tape described above. In the magnetic tape device, the recording of data on the magnetic tape and/or the reproducing of data recorded on the magnetic tape can be performed by bringing the surface of the magnetic layer of the magnetic tape into contact with the magnetic head and sliding.

In one embodiment, the magnetic tape is treated as a removable medium (a so-called interchangeable medium), and a magnetic tape cartridge accommodating the magnetic tape is inserted into and extracted from the magnetic tape device. In another aspect, the magnetic tape is not treated as an interchangeable medium, the magnetic tape is wound around a reel of a magnetic tape device including a magnetic head, and the magnetic tape is accommodated in the magnetic tape device.

In the invention and the specification, the “magnetic tape device” means a device capable of performing at least one of the recording of data on the magnetic tape or the reproducing of data recorded on the magnetic tape. Such a device is generally called a drive.

Magnetic Head

The magnetic tape device can include a magnetic head. The configuration of the magnetic head and the angle θ, which is the head tilt angle, are as described above with reference to FIGS. 1 to 3 . In a case where the magnetic head includes a reproducing element, as the reproducing element, a magnetoresistive (MR) element capable of reading information recorded on the magnetic tape with excellent sensitivity is preferable. As the MR element, various well-known MR elements (for example, a Giant Magnetoresistive (GMR) element, or a Tunnel Magnetoresistive (TMR) element) can be used. Hereinafter, the magnetic head which records data and/or reproduces the recorded data is also referred to as a “recording and reproducing head”. The element for recording data (recording element) and the element for reproducing data (reproducing element) are collectively referred to as a “magnetic head element”.

By reproducing data using the reproducing element having a narrow reproducing element width as the reproducing element, the data recorded at high density can be reproduced with high sensitivity. From this viewpoint, the reproducing element width of the reproducing element is preferably 0.8 μm or less. The reproducing element width of the reproducing element can be, for example, 0.3 μm or more. However, it is also preferable to fall below this value from the above viewpoint.

Here, the “reproducing element width” refers to a physical dimension of the reproducing element width. Such physical dimensions can be measured with an optical microscope, a scanning electron microscope, or the like.

In a case of recording data and/or reproducing recorded data, first, tracking using a servo signal can be performed. That is, as the servo signal reading element follows a predetermined servo track, the magnetic head element can be controlled to pass on the target data track. The movement of the data track is performed by changing the servo track to be read by the servo signal reading element in the tape width direction.

In addition, the recording and reproducing head can perform the recording and/or reproducing with respect to other data bands. In this case, the servo signal reading element is moved to a predetermined servo band by using the UDIM information described above, and the tracking with respect to the servo band may be started.

FIG. 5 shows an example of disposition of data bands and servo bands. In FIG. 5 , a plurality of servo bands 1 are disposed to be interposed between guide bands 3 in a magnetic layer of a magnetic tape MT. A plurality of regions 2 each of which is interposed between two servo bands are data bands. The servo pattern is a magnetized region and is formed by magnetizing a specific region of the magnetic layer by a servo write head. The region magnetized by the servo write head (position where a servo pattern is formed) is determined by standards. For example, in an LTO Ultrium format tape which is based on a local standard, a plurality of servo patterns tilted in a tape width direction as shown in FIG. 6 are formed on a servo band, in a case of manufacturing a magnetic tape. Specifically, in FIG. 6 , a servo frame SF on the servo band 1 is configured with a servo sub-frame 1 (SSF1) and a servo sub-frame 2 (SSF2). The servo sub-frame 1 is configured with an A burst (in FIG. 6 , reference numeral A) and a B burst (in FIG. 6 , reference numeral B). The A burst is configured with servo patterns Al to A5 and the B burst is configured with servo patterns B1 to B5. Meanwhile, the servo sub-frame 2 is configured with a C burst (in FIG. 6 , reference numeral C) and a D burst (in FIG. 6 , reference numeral D). The C burst is configured with servo patterns C1 to C4 and the D burst is configured with servo patterns D1 to D4. Such 18 servo patterns are disposed in the sub-frames in the arrangement of 5, 5, 4, 4, as the sets of 5 servo patterns and 4 servo patterns, and are used for recognizing the servo frames. FIG. 6 shows one servo frame for explaining. However, in practice, in the magnetic layer of the magnetic tape in which the head tracking servo in the timing-based servo system is performed, a plurality of servo frames are disposed in each servo band in a running direction. In FIG. 6 , an arrow shows a magnetic tape running direction. For example, an LTO Ultrium format tape generally includes 5,000 or more servo frames per a tape length of 1 m, in each servo band of the magnetic layer.

In the magnetic tape device, the head tilt angle can be changed while the magnetic tape is running in the magnetic tape device. The head tilt angle is, for example, an angle θ formed by the axis of the element array with respect to the width direction of the magnetic tape. The angle θ is as described above. For example, by providing an angle adjustment unit for adjusting the angle of the module of the magnetic head in the recording and reproducing head unit of the magnetic head, the angle θ can be variably adjusted during the running of the magnetic tape. Such an angle adjustment unit can include, for example, a rotation mechanism for rotating the module. For the angle adjustment unit, a well-known technology can be applied.

Regarding the head tilt angle during the running of the magnetic tape, in a case where the magnetic head includes a plurality of modules, the angle θ described with reference to FIGS. 1 to 3 can be specified for the randomly selected module. The angle θ at the start of running of the magnetic tape, ° initial, can be set to 0° or more or more than 0°. As the θ_(initial) is large, a change amount of the effective distance between the servo signal reading elements with respect to a change amount of the angle θ increases, and accordingly, it is preferable from a viewpoint of adjustment ability for adjusting the effective distance between the servo signal reading elements according to the dimension change of the width direction of the magnetic tape. From this viewpoint, the θ_(initial) is preferably 1° or more, more preferably 5° or more, and even more preferably 10° or more. Meanwhile, regarding an angle (generally referred to as a “lap angle”) formed by a surface of the magnetic layer and a contact surface of the magnetic head in a case where the magnetic tape runs and comes into contact with the magnetic head, a deviation in a tape width direction which is kept small is effective in improving uniformity of friction in the tape width direction which is generated by the contact between the magnetic head and the magnetic tape during the running of the magnetic tape. In addition, it is desirable to improve the uniformity of the friction in the tape width direction from a viewpoint of position followability and the running stability of the magnetic head. From a viewpoint of reducing the deviation of the lap angle in the tape width direction, θ_(initial) is preferably 45° or less, more preferably 40° or less, and even more preferably 35° or less.

Regarding the change of the angle θ during the running of the magnetic tape, while the magnetic tape is running in the magnetic tape device in order to record data on the magnetic tape and/or to reproduce data recorded on the magnetic tape, in a case where the angle θ of the magnetic head changes from θ_(initial) at the start of running, a maximum change amount Δθ of the angle θ during the running of the magnetic tape is a larger value among Δθ_(max) and Δθ_(min) calculated by the following equation. A maximum value of the angle θ during the running of the magnetic tape is θ_(max), and a minimum value thereof is θ_(min). In addition, “max” is an abbreviation for maximum, and “min” is an abbreviation for minimum.

Δθ_(max)=θ_(max)−θ_(initial) and

Δθ_(min)=θ_(initial)−θ_(min).

In one embodiment, the Δθ can be more than 0.000°, and is preferably 0.001° or more and more preferably 0.010° or more, from a viewpoint of adjustment ability for adjusting the effective distance between the servo signal reading elements according to the dimension change in the width direction of the magnetic tape. In addition, from a viewpoint of ease of ensuring synchronization of recorded data and/or reproduced data between a plurality of magnetic head elements during data recording and/or reproducing, the Δθ is preferably 1.000° or less, more preferably 0.900° or less, even more preferably 0.800° or less, still preferably 0.700° or less, and still more preferably 0.600° or less.

In the examples shown in FIGS. 2 and 3 , the axis of the element array is tilted toward a magnetic tape running direction. However, the present invention is not limited to such an example. The present invention also includes an aspect in which the axis of the element array is tilted in a direction opposite to the magnetic tape running direction in the magnetic tape device.

The head tilt angle θ_(initial) at the start of the running of the magnetic tape can be set by a control device or the like of the magnetic tape device.

Regarding the head tilt angle during the running of the magnetic tape, FIG. 7 is an explanatory diagram of a method for measuring the angle θ during the running of the magnetic tape. The angle θ during the running of the magnetic tape can be obtained, for example, by the following method. In a case where the angle θ during traveling on the magnetic tape is obtained by the following method, the angle θ is changed in a range of 0° to 90° during the running of the magnetic tape. That is, in a case where the axis of the element array is tilted toward the magnetic tape running direction at the start of running of the magnetic tape, the element array is not tilted so that the axis of the element array tilts toward a direction opposite to the magnetic tape running direction at the start of the running of the magnetic tape, during the running of the magnetic tape, and in a case where the axis of the element array is tilted toward the direction opposite to the magnetic tape running direction at the start of running of the magnetic tape, the element array is not tilted so that the axis of the element array tilts toward the magnetic tape running direction at the start of the running of the magnetic tape, during the running of the magnetic tape.

A phase difference (that is, time difference) AT of reproduction signals of the pair of servo signal reading elements 1 and 2 is measured. The measurement of AT can be performed by a measurement unit provided in the magnetic tape device. A configuration of such a measurement unit is well known. A distance L between a central portion of the servo signal reading element 1 and a central portion of the servo signal reading element 2 can be measured with an optical microscope or the like. In a case where a running speed of the magnetic tape is defined as a speed v, the distance in the magnetic tape running direction between the central portions of the two servo signal reading elements is set to L sin θ, and a relationship of L sin θ=v×ΔT is satisfied. Therefore, the angle θ during the running of the magnetic tape can be calculated by a formula “θ=arcsin (vΔT/L)”. The right drawing of FIG. 7 shows an example in which the axis of the element array is tilted toward the magnetic tape running direction. In this example, the phase difference (that is, time difference) ΔT of a phase of the reproduction signal of the servo signal reading element 2 with respect to a phase of the reproduction signal of the servo signal reading element 1 is measured. In a case where the axis of the element array is tilted toward the direction opposite to the running direction of the magnetic tape, θ can be obtained by the method described above, except for measuring ΔT as the phase difference (that is, time difference) of the phase of the reproduction signal of the servo signal reading element 1 with respect to the phase of the reproduction signal of the servo signal reading element 2.

For a measurement pitch of the angle θ, that is, a measurement interval of the angle θ in a tape longitudinal direction, a suitable pitch can be selected according to a frequency of tape width deformation in the tape longitudinal direction. As an example, the measurement pitch can be, for example, 250 μm.

Configuration of Magnetic Tape Device

A magnetic tape device 10 shown in FIG. 8 controls a recording and reproducing head unit 12 in accordance with a command from a control device 11 to record and reproduce data on a magnetic tape MT.

The magnetic tape device 10 has a configuration of detecting and adjusting a tension applied in a longitudinal direction of the magnetic tape from spindle motors 17A and 17B and driving devices 18A and 18B which rotatably control a magnetic tape cartridge reel and a winding reel.

The magnetic tape device 10 has a configuration in which the magnetic tape cartridge 13 can be mounted.

The magnetic tape device 10 includes a cartridge memory read and write device 14 capable of performing reading and writing with respect to the cartridge memory 131 in the magnetic tape cartridge 13.

An end portion or a leader pin of the magnetic tape MT is pulled out from the magnetic tape cartridge 13 mounted on the magnetic tape device 10 by an automatic loading mechanism or manually and passes on a recording and reproducing head through guide rollers 15A and 15B so that a surface of a magnetic layer of the magnetic tape MT comes into contact with a surface of the recording and reproducing head of the recording and reproducing head unit 12, and accordingly, the magnetic tape MT is wound around the winding reel 16.

The rotation and torque of the spindle motor 17A and the spindle motor 17B are controlled by a signal from the control device 11, and the magnetic tape MT runs at random speed and tension. A servo pattern previously formed on the magnetic tape can be used to control the tape speed and control the head tilt angle. A tension detection mechanism may be provided between the magnetic tape cartridge 13 and the winding reel 16 to detect the tension. The tension may be controlled by using the guide rollers 15A and 15B in addition to the control by the spindle motors 17A and 17B.

The cartridge memory read and write device 14 is configured to be able to read and write information of the cartridge memory 131 according to commands from the control device 11. As a communication system between the cartridge memory read and write device 14 and the cartridge memory 131, for example, an international organization for standardization (ISO) 14443 system can be used.

The control device 11 includes, for example, a controller, a storage unit, a communication unit, and the like.

The recording and reproducing head unit 12 is composed of, for example, a recording and reproducing head, a servo tracking actuator for adjusting a position of the recording and reproducing head in a track width direction, a recording and reproducing amplifier 19, a connector cable for connecting to the control device 11. The recording and reproducing head is composed of, for example, a recording element for recording data on a magnetic tape, a reproducing element for reproducing data of the magnetic tape, and a servo signal reading element for reading a servo signal recorded on the magnetic tape. For example, one or more of each of the recording elements, the reproducing element, and the servo signal reading element are mounted in one magnetic head. Alternatively, each element may be separately provided in a plurality of magnetic heads according to a running direction of the magnetic tape.

The recording and reproducing head unit 12 is configured to be able to record data on the magnetic tape MT according to a command from the control device 11. In addition, the data recorded on the magnetic tape MT can be reproduced according to a command from the control device 11.

The control device 11 has a mechanism of controlling the servo tracking actuator so as to obtain a running position of the magnetic tape from a servo signal read from a servo band during the running of the magnetic tape MT and position the recording element and/or the reproducing element at a target running position (track position). The control of the track position is performed by feedback control, for example. The control device 11 has a mechanism of obtaining a servo band spacing from servo signals read from two adjacent servo bands during the running of the magnetic tape MT. The control device 11 can store the obtained information of the servo band spacing in the storage unit inside the control device 11, the cartridge memory 131, an external connection device, and the like. In addition, the control device 11 can change the head tilt angle according to the dimensional information in the width direction of the magnetic tape during the running. Accordingly, it is possible to bring the effective distance between the servo signal reading elements closer to or match the spacing of the servo bands. The dimensional information can be obtained by using the servo pattern previously formed on the magnetic tape. For example, by doing so, the angle θ formed by the axis of the element array with respect to the width direction of the magnetic tape can be changed during the running of the magnetic tape in the magnetic tape device according to dimensional information of the magnetic tape in the width direction obtained during the running. The head tilt angle can be adjusted, for example, by feedback control. Alternatively, for example, the head tilt angle can also be adjusted by a method disclosed in JP2016-524774A or US2019/0164573A1.

EXAMPLES

Hereinafter, the invention will be described with reference to examples. However, the invention is not limited to the embodiments shown in the examples. “Parts” and “%” described below indicate “parts by mass” and “% by mass”. In addition, steps and evaluations described below are performed in an environment of an atmosphere temperature of 23° C.±1° C., unless otherwise noted. “eq” described below indicates equivalent and a unit not convertible into SI unit.

Ferromagnetic Powder

In Table 1, “BaFe” is a hexagonal barium ferrite powder (coercivity Hc: 196 kA/m, an average particle size (average plate diameter): 24 nm).

In Table 1, “SrFe1” is a hexagonal strontium ferrite powder produced by the following method.

1,707 g of SrCO₃, 687 g of H₃BO₃, 1,120 g of Fe₂O₃, 45 g of Al(OH)₃, 24 g of BaCO₃, 13 g of CaCO₃, and 235 g of Nd₂O₃ were weighed and mixed in a mixer to obtain a raw material mixture.

The obtained raw material mixture was dissolved in a platinum crucible at a melting temperature of 1,390° C., and a tap hole provided on the bottom of the platinum crucible was heated while stirring the melt, and the melt was tapped in a rod shape at approximately 6 g/sec. The tap liquid was rolled and cooled with a water cooling twin roller to prepare an amorphous body.

280 g of the prepared amorphous body was put into an electronic furnace, heated to 635° C. (crystallization temperature) at a rate of temperature rise of 3.5° C./min, and held at the same temperature for 5 hours, and hexagonal strontium ferrite particles were precipitated (crystallized).

Then, the crystallized material obtained as described above including the hexagonal strontium ferrite particles was coarse-pulverized with a mortar, 1000 g of zirconia beads having a particle diameter of 1 mm and 800 ml of an acetic acid aqueous solution having a concentration of 1% were added to a glass bottle, and a dispersion process was performed in a paint shaker for 3 hours. After that, the obtained dispersion liquid and the beads were separated and put in a stainless steel beaker. The dispersion liquid was left at a liquid temperature of 100° C. for 3 hours, subjected to a dissolving process of a glass component, precipitated with a centrifugal separator, decantation was repeated for cleaning, and drying was performed in a heating furnace at a furnace inner temperature of 110° C. for 6 hours, to obtain hexagonal strontium ferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as described above, an average particle size was 18 nm, an activation volume was 902 nm³, an anisotropy constant Ku was 2.2×10⁵ J/m³, and a mass magnetization as was 49 A·m²/kg.

12 mg of a sample powder was collected from the hexagonal strontium ferrite powder obtained as described above, the element analysis of a filtrate obtained by the partial dissolving of this sample powder under the dissolving conditions described above was performed by the ICP analysis device, and a surface layer portion content of a neodymium atom was obtained.

Separately, 12 mg of a sample powder was collected from the hexagonal strontium ferrite powder obtained as described above, the element analysis of a filtrate obtained by the total dissolving of this sample powder under the dissolving conditions described above was performed by the ICP analysis device, and a bulk content of a neodymium atom was obtained.

The content (bulk content) of the neodymium atom in the hexagonal strontium ferrite powder obtained as described above with respect to 100 atom % of iron atom was 2.9 atom %. In addition, the surface layer portion content of the neodymium atom was 8.0 atom %. A ratio of the surface layer portion content and the bulk content, “surface layer portion content/bulk content” was 2.8 and it was confirmed that the neodymium atom is unevenly distributed on the surface layer of the particles.

A crystal structure of the hexagonal ferrite shown by the powder obtained as described above was confirmed by scanning CuKα ray under the conditions of a voltage of 45 kV and intensity of 40 mA and measuring an X-ray diffraction pattern under the following conditions (X-ray diffraction analysis). The powder obtained as described above showed a crystal structure of magnetoplumbite type (M type) hexagonal ferrite. In addition, a crystal phase detected by the X-ray diffraction analysis was a magnetoplumbite type single phase.

PANalytical X'Pert Pro diffractometer, PIXcel detector

Soller slit of incident beam and diffraction beam: 0.017 radians

Fixed angle of dispersion slit: ¼ degrees

Mask: 10 mm

Scattering prevention slit: ¼ degrees

Measurement mode: continuous

Measurement time per 1 stage: 3 seconds

Measurement speed: 0.017 degrees per second

Measurement step: 0.05 degree

In Table 1, “SrFe2” is a hexagonal strontium ferrite powder produced by the following method.

1,725 g of SrCO₃, 666 g of H₃BO₃, 1,332 g of Fe₂O₃, 52 g of Al(OH)₃, 34 g of CaCO₃, and 141 g of BaCO₃ were weighed and mixed in a mixer to obtain a raw material mixture.

The obtained raw material mixture was dissolved in a platinum crucible at a melting temperature of 1,380° C., and a tap hole provided on the bottom of the platinum crucible was heated while stirring the melt, and the melt was tapped in a rod shape at approximately 6 g/sec. The tap liquid was rolled and cooled with a water cooling twin roller to prepare an amorphous body.

280 g of the obtained amorphous body was put into an electronic furnace, heated to 645° C. (crystallization temperature), and held at the same temperature for 5 hours, and hexagonal strontium ferrite particles were precipitated (crystallized).

Then, the crystallized material obtained as described above including the hexagonal strontium ferrite particles was coarse-pulverized with a mortar, 1000 g of zirconia beads having a particle diameter of 1 mm and 800 ml of an acetic acid aqueous solution having a concentration of 1% were added to a glass bottle, and a dispersion process was performed in a paint shaker for 3 hours. After that, the obtained dispersion liquid and the beads were separated and put in a stainless steel beaker. The dispersion liquid was left at a liquid temperature of 100° C. for 3 hours, subjected to a dissolving process of a glass component, precipitated with a centrifugal separator, decantation was repeated for cleaning, and drying was performed in a heating furnace at a furnace inner temperature of 110° C. for 6 hours, to obtain hexagonal strontium ferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as described above, an average particle size was 19 nm, an activation volume was 1,102 nm³, an anisotropy constant Ku was 2.0×10⁵ J/m³, and a mass magnetization σs was 50 A×m²/kg.

In Table 1, “ε-iron oxide” is an ε-iron oxide powder produced by the following method.

4.0 g of ammonia aqueous solution having a concentration of 25% was added to a material obtained by dissolving 8.3 g of iron (III) nitrate nonahydrate, 1.3 g of gallium (III) nitrate octahydrate, 190 mg of cobalt (II) nitrate hexahydrate, 150 mg of titanium (IV) sulfate, and 1.5 g of polyvinyl pyrrolidone (PVP) in 90 g of pure water, while stirring by using a magnetic stirrer, in an atmosphere under the conditions of an atmosphere temperature of 25° C., and the mixture was stirred for 2 hours still under the temperature condition of the atmosphere temperature of 25° C. A citric acid aqueous solution obtained by dissolving 1 g of citric acid in 9 g of pure water was added to the obtained solution and stirred for 1 hour. The powder precipitated after the stirring was collected by centrifugal separation, washed with pure water, and dried in a heating furnace at a furnace inner temperature of 80° C.

800 g of pure water was added to the dried powder and the powder was dispersed in water again, to obtain a dispersion liquid. The obtained dispersion liquid was heated to a liquid temperature of 50° C., and 40 g of ammonia aqueous solution having a concentration of 25% was added dropwise while stirring. The stirring was performed for 1 hour while holding the temperature of 50° C., and 14 mL of tetraethoxysilane (TEOS) was added dropwise and stirred for 24 hours. 50 g of ammonium sulfate was added to the obtained reaction solution, the precipitated powder was collected by centrifugal separation, washed with pure water, and dried in a heating furnace at a furnace inner temperature of 80° C. for 24 hours, and a precursor of ferromagnetic powder was obtained.

The heating furnace at a furnace inner temperature of 1,000° C. was filled with the obtained precursor of ferromagnetic powder in the atmosphere and subjected to heat treatment for 4 hours.

The heat-treated precursor of ferromagnetic powder was put into sodium hydroxide (NaOH) aqueous solution having a concentration of 4 mol/L, the liquid temperature was held at 70° C., stirring was performed for 24 hours, and accordingly, a silicon acid compound which was an impurity was removed from the heat-treated precursor of ferromagnetic powder.

After that, by the centrifugal separation process, ferromagnetic powder obtained by removing the silicon acid compound was collected and washed with pure water, and ferromagnetic powder was obtained.

The composition of the obtained ferromagnetic powder was confirmed by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), and Ga, Co, and Ti substitution type ε-iron oxide (ε-Ga_(0.28)Co_(0.05)Ti_(0.05)Fe_(1.62)O₃) was obtained. In addition, the X-ray diffraction analysis was performed under the same conditions as disclosed regarding SrFe1 above, and it was confirmed that the obtained ferromagnetic powder has a crystal structure of a single phase which is an ε phase not including a crystal structure of an α phase and a γ phase (ε-iron oxide type crystal structure) from the peak of the X-ray diffraction pattern.

Regarding the obtained (ε-iron oxide powder, an average particle size was 12 nm, an activation volume was 746 nm³, an anisotropy constant Ku was 1.2×10⁵ J/m³, and a mass magnetization σs was 16 A×m²/kg.

The activation volume and the anisotropy constant Ku of the hexagonal strontium ferrite powder and the ε-iron oxide powder are values obtained by the method described above regarding each ferromagnetic powder by using an oscillation sample type magnetic-flux meter (manufactured by Toei Industry Co., Ltd.).

The mass magnetization σs is a value measured using an oscillation sample type magnetic-flux meter (manufactured by Toei Industry Co., Ltd.) at a magnetic field strength of 15 kOe.

Example 1

(1) List of Magnetic Layer Forming Composition

Magnetic Liquid

Ferromagnetic powder (see Table 1): 100.0 parts

SO₃Na group-containing polyurethane resin: 14.0 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.4 meq/g

Cyclohexanone: 150 parts

Methyl ethyl ketone: 150 parts

Abrasive solution A

Alumina abrasive (average particle size: 100 nm): 3.0 parts

Sulfonic acid group-containing polyurethane resin: 0.3 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.3 meq/g

Cyclohexanone: 26.7 parts

Abrasive solution B

Diamond abrasive (average particle size: 100 nm): 1.0 part

Sulfonic acid group-containing polyurethane resin: 0.1 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.3 meq/g

Cyclohexanone: 26.7 parts

Silica Sol

Colloidal silica (average particle size: 100 nm): 0.2 part

Methyl ethyl ketone: 1.4 parts

Other Components

Stearic acid: 2.0 parts

Butyl stearate: 10.0 parts

Polyisocyanate (CORONATE manufactured by Nippon Polyurethane Industry Co., Ltd.): 2.5 parts

Cyclohexanone: 200.0 parts

Methyl ethyl ketone: 200.0 parts

(2) List of Non-Magnetic Layer Forming Composition

Non-magnetic inorganic powder (α-iron oxide): 100.0 parts

Average particle size (average major axis length): 10 nm

Average acicular ratio: 1.9

Brunauer-emmett-teller (BET) specific surface area: 75 m²/g

Carbon black: 25.0 parts

Average particle size: 20 nm

SO₃Na group-containing polyurethane resin: 18 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g

Stearic acid: 1.0 part

Cyclohexanone: 300.0 parts

Methyl ethyl ketone: 300.0 parts

(3) List of back coating layer forming composition

Carbon black: 100.0 parts

BP-800 manufactured by Cabot Corporation, average particle size: 17 nm

SO₃Na group-containing polyurethane resin (SO₃Na group: 70 eq/ton): 20.0 parts

OSO₃K group-containing vinyl chloride resin (OSO₃K group: 70 eq/ton): 30.0 parts

Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd., number average molecular weight: 600): see Table 1

Stearic acid: see Table 1

Cyclohexanone: 140.0 parts

Methyl ethyl ketone: 170.0 parts

Butyl stearate: 2.0 parts

Stearic acid amide: 0.1 parts

(4) Preparation of Each Layer Forming Composition

For the magnetic layer forming composition, a magnetic liquid was prepared by dispersing the components of the magnetic liquid with a batch type vertical sand mill for 24 hours. As dispersion beads, zirconia beads having a bead diameter of 0.5 mm were used.

Regarding the abrasive solution, the above components of the abrasive solution A and the abrasive solution B were dispersed for 24 hours with a batch type ultrasonic device (20 kHz, 300 W), respectively, to obtain the abrasive solution A and the abrasive solution B.

The magnetic liquid, the abrasive solution A and the abrasive solution B were mixed with the above silica sol and other components, and then dispersed in a batch type ultrasonic device (20 kHz, 300 W) for 30 minutes. After that, the obtained mixed solution was filtered by using a filter having a hole diameter of 0.5 μm, and the magnetic layer forming composition was prepared.

For the non-magnetic layer forming composition, the components were dispersed by using a batch type vertical sand mill for 24 hours. As dispersion beads, zirconia beads having a bead diameter of 0.1 mm were used. The obtained dispersion liquid was filtered with a filter having a hole diameter of 0.5 μm, and a non-magnetic layer forming composition was prepared.

Regarding the back coating layer forming composition, the above components were kneaded with a continuous kneader and then dispersed using a sand mill. After adding 40.0 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.) and 1,000.0 parts of methyl ethyl ketone to the obtained dispersion liquid, the mixture was filtered using a filter having a hole diameter of 1 μm to prepare a back coating layer forming composition.

(5) Manufacturing of Magnetic Tape and Magnetic Tape Cartridge

A magnetic tape was manufactured according to the manufacturing step shown in FIG. 4 . The details are as follows.

A support made of polyethylene naphthalate having a thickness of 4.1 μm was sent from the sending part, and the non-magnetic layer forming composition was applied to one surface thereof so that the thickness after the drying is 0.7 μm in the first coating part to form a coating layer. The cooling step was performed by passing the formed coating layer through the cooling zone in which the atmosphere temperature was adjusted to 0° C. for the retention time shown in Table 1 while the coating layer was wet, and then the heating and drying step was performed by passing the coating layer through the first heat treatment zone at the drying temperature (the atmosphere temperature, the same applies hereinafter) shown in Table 1, to form a non-magnetic layer.

Then, the magnetic layer forming composition prepared as described above was applied onto the non-magnetic layer so that the thickness after the drying is 0.1 μm in the second coating part, and a coating layer was formed. A homeotropic alignment process was performed in the alignment zone by applying a magnetic field having a magnetic field strength of 0.3 T to the surface of the coating layer of the magnetic layer forming composition in a vertical direction while the coating layer was wet, and the coating layer was dried in the second heat treatment zone at the drying temperature shown in Table 1.

After that, in the third coating part, the back coating layer forming composition prepared as described above was applied to the surface of the non-magnetic support made of polyethylene naphthalate on a side opposite to the surface where the non-magnetic layer and the magnetic layer are formed, so that the thickness after the drying becomes 0.3 μm, to form a coating layer, and the formed coating layer was dried in a third heat treatment zone at the drying temperature shown in Table 1.

After that, a calendar treatment (surface smoothing treatment) was performed under the calendar treatment conditions shown in Table 1 using a calendar roll composed of only a metal roll.

Then, the heat treatment was performed in the environment of the atmosphere temperature of 70° C. for 36 hours. After the heat treatment, the magnetic tape was manufactured by slitting to have a width of ½ inches.

In a state where the magnetic layer of the manufactured magnetic tape is demagnetized, by recording a servo signal on a magnetic layer with a commercially available servo writer, the magnetic tape including a data band, a servo band, and a guide band in the disposition according to a linear-tape-open (LTO) Ultrium format, and including a servo pattern (timing-based servo pattern) having the disposition and shape according to the LTO Ultrium format on the servo band was obtained. The servo pattern formed by doing so is a servo pattern disclosed in Japanese Industrial Standards (JIS) X6175:2006 and Standard ECMA-319 (June 2001). The total number of servo bands is five, and the total number of data bands is four.

A magnetic tape (length of 960 m) on which the servo signal was recorded as described above was wound around the reel of the magnetic tape cartridge (LTO Ultrium 8 data cartridge), and a leader tape according to Article 9 of Section 3 of standard European Computer Manufacturers Association (ECMA)-319 (June 2001) was bonded to an end thereof by using a commercially available splicing tape.

By doing so, a magnetic tape cartridge in which the magnetic tape was wound around the reel was manufactured.

It can be confirmed by the following method that the back coating layer of the magnetic tape contains a compound formed of polyethyleneimine and stearic acid and having an ammonium salt structure of an alkyl ester anion represented by Formula 1.

A sample is cut out from a magnetic tape, and X-ray photoelectron spectroscopy is performed on the surface of the back coating layer (measurement area: 300 μm×700 μm) using an ESCA device. Specifically, wide scan measurement is performed by the ESCA device under the following measurement conditions. In the measurement results, peaks are confirmed at a position of a binding energy of the ester anion and a position of a binding energy of the ammonium cation.

Device: AXIS-ULTRA manufactured by Shimadzu Corporation

Excited X-ray source: Monochromatic Al-Kα ray

Scan range: 0 to 1,200 eV

Pass energy: 160 eV

Energy resolution: 1 eV/step

Capturing Time: 100 ms/step

Number of times of integration: 5

In addition, a sample piece having a length of 3 cm is cut out from the magnetic tape, and attenuated total reflection-fourier transform-infrared spectrum (ATR-FT-IR) measurement (reflection method) is performed on the surface of the back coating layer, and, in the measurement result, the absorption is confirmed on a wave number corresponding to absorption of COO⁻ (1,540 cm⁻¹ or 1,430 cm⁻¹) and a wave number corresponding to the absorption of the ammonium cation (2,400 cm⁻¹).

Examples 2 to 17 and Comparative Examples 1 to 9

A magnetic tape and a magnetic tape cartridge were obtained by the method described in Example 1, except that the items shown in Table 1 were changed as shown in Table 1.

In Table 1, in the comparative examples in which “none” is disclosed in a column of the cooling zone retention time, a magnetic tape was manufactured by a manufacturing step not including the cooling zone in the non-magnetic layer forming step.

For each example and each comparative example, two magnetic tape cartridges were manufactured, one was used for evaluation of recording and reproducing performance and the other was used for other evaluations.

Evaluation Method

Number of Recesses, Width Direction σ of Number of Recesses

The following conditions were used as measurement conditions of the AFM, and by the method described above, the number of recesses having an equivalent circle diameter of 0.30 μm to 0.60 μm (per 40 μm×40 μm area) on the surface of the magnetic layer of the magnetic tape and the width direction σ of the number of recesses were obtained.

The measurement regarding a region of the surface of the magnetic layer of the magnetic tape having an area of 40 μm×40 μm is performed with an AFM (Nanoscope 5 manufactured by BRUKER Corporation) in a peak force tapping mode. SCANASYST-AIR manufactured by BRUKER Corporation is used as a probe, a resolution is set as 512 pixels×512 pixels, and a scan speed is set by the measurement regarding 1 screen (512 pixels×512 pixels) for 512 seconds.

Total thickness of Magnetic Tape (Tape Thickness)

10 tape samples (length: 5 cm) were cut out from any part of each of the magnetic tape of Examples and Comparative Examples, and these tape samples were stacked to measure the thickness. The thickness was measured using a digital thickness gauge of a Millimar 1240 compact amplifier manufactured by MARH and a Millimar 1301 induction probe. The value (thickness per tape sample) obtained by calculating 1/10 of the measured thickness was defined as the tape thickness. For all of the magnetic tape, the tape thickness was 5.2

Recording and Reproducing Performance

Using each of the magnetic tape cartridges of the examples and the comparative examples, data recording and reproducing were performed using the magnetic tape device having the configuration shown in FIG. 8 . The arrangement order of the modules included in the recording and reproducing head mounted on the recording and reproducing head unit is “recording module-reproducing module-recording module” (total number of modules: 3). The number of magnetic head elements in each module is 32 (Ch0 to Ch31), and the element array is configured by sandwiching these magnetic head elements between the pair of servo signal reading elements. The reproducing element width of the reproducing element included in the reproducing module is 0.8 μm.

The head tilt angle during the recording was set as 0° and the head tilt angle during the reproducing was set as 5°. The head tilt angle is an angle θ formed by the axis of the element array of the reproducing module with respect to the width direction of the magnetic tape during the recording and reproducing. The angle θ was set by the control device of the magnetic tape device respectively at the start of the recording and at the start of the reproducing, and the head tilt angle was fixed respectively during the running of the magnetic tape during the recording and during the running of the magnetic tape during the reproducing. In this evaluation, since the head tilt angle is different during the recording and the reproducing, the head tilt angle during the data recording is different from the head tilt angle during the data reading (that is, during the reproducing) for each recording bit.

The number of reproducing elements (number of channels) in the reproducing described above is 32 channels. In a case where all the data of 32 channels were correctly read during the reproducing, the recording and reproducing performance is evaluated as “3”, in a case where data of 31 to 28 channels were correctly read, the recording and reproducing performance is evaluated as “2”, and in other cases, the recording and reproducing performance is evaluated as “1”.

The result described above is shown in Table 1 (Tables 1-1 to 1-3).

TABLE 1-1 Comparative Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 F 

 powder Typc BaFe BaFe BaFe BaFe BaFe Back coating layer Polyethyl 

0.2 0.3 0.3 0.5 1.0

 

Stearic acid 0.4 0.5 0.7 1.0 2.0 Coating Cooling zone  

1 second 1 second 1 second 1 second 1 second time Drying temperature First heat treatment  

105° C. 105° C. 105° C. 105° C. 105° C. Second heat treatment 105° C. 105° C. 105° C. 105° C. 105° C. zone Third heat treatment zone 105° C. 105° C. 105° C. 105° C. 105° C. Calendar process Temperature 100° C. 100° C. 100° C. 100° C. 100° C. condition Linear pressure 310 kNm 320 kNm 320 kNm 320 kNm 320 kNm Speed 75 m/min 70 m/min 70 m/min 70 m/min 70 m/min Number of  

600 400 300 200 100 Width direction  

 of 100 90 75

number of  

Recording and 2 2 2 2 2 reproducing performance Comparative Comparative Comparative Comparative Example 6 Example 7 Example 8 Example 9 F 

 powder Typc BaFe BaFe BaFe BaFe Back coating layer Polyethyl 

2.7 0.2 0.2 0.3

 

Stearic acid 5.3 0.4 0.4 0.7 Coating Cooling zone  

1 second 5 seconds 10 seconds 5 seconds time Drying temperature First heat treatment  

105° C. 105° C. 105° C. 105° C. Second heat treatment 105° C. 105° C. 105° C. 105° C. zone Third heat treatment zone 105° C. 105° C. 105° C. 105° C. Calendar process Temperature 100° C. 105° C. 110° C. 105° C. condition Linear pressure 320 kNm 320 kNm 350 kNm 320 kNm Speed 70 m/min 60 m/min 60 m/min 60 m/min Number of  

10 500 500 300 Width direction  

 of 5 80 60 50 number of  

Recording and

2 2 2 reproducing performance

indicates data missing or illegible when filed

TABLE 1-2 Comparative Comparative Comparative Comparative Example 10 Example 11 Example 12 Example 13 F 

 powder Typc BaFe BaFe BaFe BaFe Back coating layer Polyethyl 

0.3 1.0 1.0

 

Stearic acid

2.0 2.0 5.3 Coating Cooling zone  

10 seconds 5 seconds 10 seconds 5 seconds time Drying temperature First heat treatment  

105° C. 105° C. 105° C. 105° C. Second heat treatment 105° C. 105° C. 105° C. 105° C. zone Third heat treatment zone 105° C. 105° C. 105° C. 105° C. Calendar process Temperature 110° C. 105° C. 110° C. 105° C. condition Linear pressure 350 kNm 120 kNm 150 kNm 320 kNm Speed 60 m/min 60 m/min 60 m/min 60 m/min Number of  

300 100 100 10 Width direction  

 of 40 20 10 4 number of  

Recording and 2 3 3 3 reproducing performance Comparative Comparative Comparative Comparative Example 14 Example 15 Example 16 Example 17 F 

 powder Typc BaFe

Back coating layer Polyethyl 

0.2 0.2 0.2

 

Stearic acid 5.3 0.4 0.4 0.4 Coating Cooling zone  

10 seconds 1 second 1 second 1 second time Drying temperature First heat treatment  

105° C. 105° C. 105° C. 105° C. Second heat treatment 105° C. 105° C. 105° C. 105° C. zone Third heat treatment zone 105° C. 105° C. 105° C. 105° C. Calendar process Temperature 110° C. 100° C. 100° C. 100° C. condition Linear pressure 350 kNm 110 kNm 310 kNm 310 kNm Speed 60 m/min 75 m/min 75 m/min 75 m/min Number of  

10 600 600 600 Width direction  

 of 3 100 100 100 number of  

Recording and 3 2 2 2 reproducing performance

indicates data missing or illegible when filed

TABLE 1-3 Comparative Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 F 

 powder Typc BaFe BaFe BaFe BaFe BaFe Back coating layer Polyethyl 

0 0 0.1 0.2 4.0

 

Stearic acid 0 0.1 0.1 0.4 8.0 Coating Cooling zone  

None None None None None time Drying temperature First heat treatment  

80° C. 80° C. 80° C. 80° C. 80° C. Second heat treatment 80° C. 80° C. 80° C. 80° C. 80° C. zone Third heat treatment zone 80° C. 80° C. 80° C. 80° C. 80° C. Calendar process Temperature 90° C. 90° C. 90° C. 90° C. 90° C. condition Linear pressure 294 kNm 294 kNm 294 kNm 294 kNm 294 kNm Speed 80 m/min 80 m/min 80 m/min 80 m/min 80 m/min Number of  

2000 1500 1000 700 5 Width direction  

 of 500 400 150 300 2 number of  

Recording and 1 1 1 1 1 reproducing performance Comparative Comparative Comparative Comparative Example 6 Example 7 Example 8 Example 9 F 

 powder Typc BaFe BaFe BaFe BaFe Back coating layer Polyethyl 

5.3 0.2 0.3 0.3

 

Stearic acid 10.7 0.4 0.5 0.7 Coating Cooling zone  

None None None None time Drying temperature First heat treatment  

80° C. 80° C. 80° C. 80° C. Second heat treatment 80° C. 80° C. 80° C. 80° C. zone Third heat treatment zone 80° C. 80° C. 80° C. 80° C. Calendar process Temperature 90° C. 90° C. 90° C. 90° C. condition Linear pressure 294 kNm 294 kNm 294 kNm 294 kNm Speed 80 m/min 80 m/min 80 m/min 80 m/min Number of  

3 500 400 300 Width direction  

 of 1 200 150 120 number of  

Recording and 1 1 1 1 reproducing performance

indicates data missing or illegible when filed

A magnetic tape cartridge was manufactured by the method described as in Example 1 except that the homeotropic alignment process was not performed in a case of manufacturing the magnetic tape.

A sample piece was cut out from the magnetic tape taken out from the magnetic tape cartridge. For this sample piece, a vertical squareness ratio SQ was obtained by the method described above using a TM-TRVSM5050-SMSL type manufactured by Tamagawa Seisakusho Co., Ltd. as an oscillation sample type magnetic-flux meter and it was 0.55.

The magnetic tape was also taken out from the magnetic tape cartridge of Example 1, and the vertical squareness ratio was obtained in the same manner for the sample piece cut out from the magnetic tape, and it was 0.60.

The magnetic tapes taken out from the above two magnetic tape cartridges were attached to each of the ½-inch reel testers, and the electromagnetic conversion characteristics (signal-to-noise ratio (SNR)) were evaluated by the following methods. As a result, regarding the magnetic tape taken out from the magnetic tape cartridge of Example 1, a value of SNR 2 dB higher than that of the magnetic tape manufactured without the homeotropic alignment process was obtained.

In an environment of a temperature of 23° C. and a relative humidity of 50%, a tension of 0.7 Newton (N) was applied in the longitudinal direction of the magnetic tape, and recording and reproduction were performed for 10 passes. A relative speed of the magnetic head and the magnetic tape was set as 6 m/sec. The recording was performed by using a metal-in-gap (MIG) head (gap length of 0.15 μm, track width of 1.0 μm) as the recording head and by setting a recording current as an optimal recording current of each magnetic tape. The reproduction was performed using a giant-magnetoresistive (GMR) head (element thickness of 15 nm, shield interval of 0.1 μm, reproducing element width of 0.8 μm) as the reproduction head. The head tilt angle was set to 0°. A signal having a linear recording density of 300 kfci was recorded, and the reproduction signal was measured with a spectrum analyzer manufactured by ShibaSoku Co., Ltd. In addition, the unit kfci is a unit of linear recording density (cannot be converted to SI unit system). As the signal, a sufficiently stabilized portion of the signal after starting the running of the magnetic tape was used.

One aspect of the invention is advantageous in a technical field of various data storages. 

What is claimed is:
 1. A magnetic tape comprising: a non-magnetic support; a magnetic layer including a ferromagnetic powder a non-magnetic support; and a magnetic layer containing a ferromagnetic powder, wherein the number of recesses having an equivalent circle diameter of 0.30 μm to 0.60 μm existing on a surface of the magnetic layer is 10 to 600 per 40 μm×40 μm area, and a standard deviation σ of the number of recesses in a width direction on the surface of the magnetic layer is 100 or less.
 2. The magnetic tape according to claim 1, wherein the number of the recesses is 10 to
 100. 3. The magnetic tape according to claim 1, wherein the standard deviation σ of the number of recesses is 20 or less.
 4. The magnetic tape according to claim 2, wherein the standard deviation σ of the number of recesses is 20 or less.
 5. The magnetic tape according to claim 1, wherein a vertical squareness ratio of the magnetic tape is 0.60 or more.
 6. The magnetic tape according to claim 4, wherein a vertical squareness ratio of the magnetic tape is 0.60 or more.
 7. The magnetic tape according to claim 1, further comprising: a non-magnetic layer containing a non-magnetic powder between the non-magnetic support and the magnetic layer.
 8. The magnetic tape according to claim 1, further comprising: a back coating layer containing a non-magnetic powder on a surface side of the non-magnetic support opposite to a surface side provided with the magnetic layer.
 9. The magnetic tape according to claim 1, wherein a tape thickness is 5.2 μm or less.
 10. The magnetic tape according to claim 2, wherein a tape thickness is 5.2 μm or less.
 11. The magnetic tape according to claim 3, wherein a tape thickness is 5.2 μm or less.
 12. The magnetic tape according to claim 4, wherein a tape thickness is 5.2 μm or less.
 13. The magnetic tape according to claim 5, wherein a tape thickness is 5.2 μm or less.
 14. The magnetic tape according to claim 6, wherein a tape thickness is 5.2 μm or less.
 15. A magnetic tape cartridge comprising: the magnetic tape according to claim
 1. 16. The magnetic tape cartridge according to claim 15, wherein the number of the recesses is 10 to 100, the standard deviation σ of the number of recesses is 20 or less, a vertical squareness ratio of the magnetic tape is 0.60 or more, and a tape thickness of the magnetic tape is 5.2 μm or less.
 17. A magnetic tape device comprising: the magnetic tape according to claim
 1. 18. The magnetic tape device according to claim 17, further comprising: a magnetic head, wherein the magnetic head includes a module including an element array having a plurality of magnetic head elements between a pair of servo signal reading elements, and the magnetic tape device changes an angle θ formed by an axis of the element array with respect to the width direction of the magnetic tape during running of the magnetic tape in the magnetic tape device.
 19. The magnetic tape device according to claim 17, wherein the number of the recesses is 10 to 100, the standard deviation σ of the number of recesses is 20 or less, a vertical squareness ratio of the magnetic tape is 0.60 or more, and a tape thickness of the magnetic tape is 5.2 μm or less. 